Systems and methods for assessing the effectiveness of a therapy including a drug regimen using an implantable medical device

ABSTRACT

Systems and methods rely on feedback from an active medical device or devices (e.g., neurostimulator coupled to sensing and stimulation elements such as electrodes) to assess the effectiveness of a patient&#39;s drug regimen. Such reliance may include analyzing characteristics in physiological data acquired by the medical device(s), for example, in the form of responses evoked from the patient by electrical stimulation waveforms. Systems and methods further involved adjusting one or more parameters according to which a combination therapy consisting of at least a drug regimen and an electrical stimulation therapy are delivered to a patient, in an effort to optimize the therapeutic effect of the combination. The adjustments may be automatically by one or more implanted or external hosts working together or alone, and/or with the input of a physician.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. application Ser. No. 13/539,301filed on Jun. 30, 2012, entitled “Systems and Methods for Assessing theEffectiveness of a Therapy Including a Drug Regimen Using an ImplantableMedical Device,” which claims priority to and benefit of U.S.Provisional Patent Application No. 61/504,164 filed Jul. 1, 2011,entitled “Systems and Methods for Treating Neurological Disorders UsingNeurostimulation and Drugs,” each of which is expressly incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

Embodiments generally relate to systems and methods for using animplantable medical device in combination with a drug therapy to treat adisorder or condition of the central nervous system.

BACKGROUND

Physicians often treat patients who suffer from a neurological disorderor otherwise present with an undesirable or unwanted neurologicalcondition with a drug regimen in an effort to modulate the behavior ofthe central nervous system. A physician's choice of a drug or drugs touse and the dosage of each drug may be based on prior experience withthe drug(s) and dosage(s) for patients who have been diagnosed with thesame disorder or who present with the same condition. Often, however,the degree to which a drug regimen is or is not effective for aparticular patient may depend on factors that are specific to thatpatient. Two patients with the same neurological disorder may not beequally well served by the same dose of the same drug, in terms of, forexample, tolerance or efficacy. In addition, even when a drug regimen iswell tolerated and effective for a given patient some of the time, itmay not be well tolerated or effective all of the time.

Implantable medical devices are available or under investigation thatenable physicians to treat patients who suffer from a neurologicaldisorder with electrical stimulation therapy. A physician may treat apatient who has been implanted with a neurostimulator with bothelectrical stimulation therapy and a drug regimen in an effort tomodulate the behavior of the central nervous system

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a patient's head in which animplantable medical device has been implanted.

FIG. 2A is a schematic representation of an electrode-bearing corticalstrip lead that may be used for sensing physiological signals and/ordelivering electrical stimulation to a patient.

FIG. 2B is a schematic representation of an electrode-bearing depth ordeep brain lead that may be used for sensing physiological signalsand/or delivering electrical stimulation to a patient.

FIG. 3 is s block diagram illustrating some of the components andfeatures of a neurostimulation system.

FIG. 4A is a time series graphical representation of an electrographicsignal of the type that might be monitored by and acquired by accordingto embodiments.

FIG. 4B is another time series graphical representation of anelectrographic signal of the type that might be monitored by andacquired by according to embodiments,

FIG. 5A is a diagram illustrating examples of the characteristics of anelectrical stimulation therapy that may be generated and outputaccording to embodiments.

FIG. 5B is a further diagram illustrating examples of thecharacteristics of an electrical stimulation therapy that may begenerated and output according to embodiments

FIG. 5C is another diagram illustrating examples of the characteristicsof an electrical stimulation therapy that may be generated and outputaccording to embodiments.

FIG. 6 is a flow chart corresponding to embodiments.

FIG. 7 is a schematic illustrating a system according to someembodiments.

FIG. 8 is a graphical representation illustrating an assessment of theeffectiveness of a drug regimen according to embodiments.

FIG. 9 is a graphical representation illustrating another assessment ofthe effectiveness of a drug regimen according to embodiments.

FIG. 10 is a graphical representation of evoked responses.

FIG. 11 is a graphical representation illustrating an assessment of theeffectiveness of a drug regimen according to embodiments.

FIG. 12A is a graphical representation of a power value plotted versustime associated with a signal sensed from a patient.

FIG. 12B is a spectrogram corresponding to the plot of FIG. 12A.

FIG. 13 is a schematic diagram including a display that might beassociated with some embodiments.

FIG. 14 is another flow chart corresponding to embodiments.

FIG. 15 is a further flow chart corresponding to embodiments.

FIG. 16 is a still another flow chart corresponding to embodiments.

FIG. 17 is yet another flow chart corresponding to embodiments.

FIG. 18 is a flow chart corresponding to embodiments.

FIG. 19 is another flow chart corresponding to embodiments.

FIG. 20 is further flow chart corresponding to embodiments.

FIG. 21 is a schematic illustration of a patient's head in which a brainlead associated with a drug reservoir and another implantable medicaldevice has been implanted.

The drawings referred to in this description should not be understood asbeing drawn to scale unless specifically noted.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. While the technology willbe described in conjunction with various embodiment(s), it will beunderstood that they are not intended to be limited to theseembodiments. On the contrary, the present technology is intended tocover alternatives, modifications and equivalents, which may be includedwithin the various embodiments as defined by the appended claims.

Furthermore, in the following detailed description, numerous specificdetails are set forth in order to provide a thorough understanding ofembodiments. However, embodiments may be practiced without thesespecific details. In other instances, well known methods, procedures,components, and circuits have not been described in detail as not tounnecessarily obscure aspects of embodiments.

Embodiments of systems and methods are described in which theeffectiveness of a drug therapy to which a patient is subjected in orderto treat or otherwise affect a neurological disorder or otherneurological condition (hereinafter collectively referred to as“neurological disorder” or “disorder” for ease of reference but not byway of limitation) is measured relative to information acquired,processed, and analyzed by an implantable medical device.

Some embodiments provide for presenting information derived from theimplantable medical device about the effectiveness of the drug therapyto the physician so that the physician may make adjustments to one ormore the of the parameters that define the drug therapy (e.g., type ofdrug(s), dosage of drug(s), class of each drug, method of delivery ofeach drug, timing of delivery of each drug, etc.) with an objective ofincreasing the effectiveness of the drug therapy in treating thedisorder. These embodiments rely, in part, on the capability of theimplanted medical device to acquire, process, and analyze physiologicaldata obtained from specific sensing locations in the patient's centralnervous systems.

In other embodiments, information derived from the implanted medicaldevice relating to the effectiveness of one drug therapy may be used toadjust either one or more parameters of that drug therapy to which thepatient is subjected or, alternatively or additionally, to introduceanother therapy to the patient that will be used, together with thefirst drug therapy to treat the patient. These embodiments rely, inpart, on the capability of the implanted medical device to elucidatesynergistic (or antagonistic) relationships between a drug therapy towhich the patient is subjected and another therapy to which the patientmay be or already also is subjected.

By way of example, an additional therapy may be one that is designed tomodulate the behavior of the patient's central nervous system in thesame or a different way than is a first drug therapy and may include,for example, a form of electrical stimulation therapy or a form ofoptical stimulation. An additional therapy may also include a form ofdrug therapy that is different than the form of a first drug therapy(e.g., the first drug therapy may include a pill administered orally,and the additional therapy may include a drug delivered directly to adesired location in the patient's brain (e.g., via a needle or acatheter or an active implant configured to controllably deliver a drugfrom, for instance, a drug reservoir)).

In still other embodiments, information derived from the implantedmedical device relating to the effectiveness of a drug therapy may beused to change one or more parameters of an additional therapy thepatient is receiving (e.g., if the patient is receiving electricalstimulation therapy in addition to the drug therapy, the informationderived from the implanted medical device may be used to adjust one ormore parameters of the electrical stimulation therapy in an effort toimprove the response of the patient to the combination of the drugtherapy and the electrical stimulation therapy).

In yet further embodiments, information derived from the implantedmedical device may be used to adjust one or more parameters of any ofmultiple therapies the patient is receiving or may receive, in an effortto achieve an optimum efficacious result from the combination oftherapies.

In some cases where adjusting of parameters occurs, the adjustment maybe initiated and undertaken automatically, for example, using one ormore algorithms and outputs generated by the implantable medical deviceor from a different implantable medical device or some other source of aform of therapy. In other cases, an adjustment may be initiated by aphysician and then undertaken by implementing the adjustment using animplantable medical device or other source of a form of therapy. Instill other cases, the adjustment may be initiated by the physician andundertaken by the patient (e.g., when the adjustment is to take adifferent pill or take the same or a different pill at a different timeof day).

The discussion that follows will describe the structure andfunctionality of embodiments.

FIG. 1 is a schematic illustration of patient's head in which theimplantable components of an implantable medical system according tosystems and methods of the embodiments have been implanted andrepresentations of movement and targeting of a systemically-delivereddrug or medication are indicated using arrows and dashed lines.

Generally, physicians often treat patients with a disorder of thenervous system using one or more medications in an effort to helpcontrol the disorder. These medications usually are believed to modulatethe behavior of the nervous system in some way. How a given drugmodulates nervous system behavior may depend, in part, on circumstancesat one or more localized areas in the nervous system or functionalcircuits in the brain. These circumstances can include variables relatedto local functioning of the neural tissue (i.e., neurophysiology), suchas the overall number of action potentials occurring within a region(i.e., neural activity or neural firing); the type of action potentials,such as inhibitory or excitatory; or the temporal or spatial pattern ofaction potentials. These circumstances may also include variables suchas regional cerebral blood flow or fraction of oxygenated hemoglobinrelated to other physiological processes such as hemodynamics. Ofcourse, the action of a drug also may be affected by other conditions ofthe patient and whether the patient is also receiving some other form oftherapy to treat the disorder, such as electrical stimulation therapy.

Medications for diseases of the nervous system commonly are takensystemically. However, the physician may hope and expect that the drugwill have a particular effect at a certain location or functionalcircuit in the nervous system or a part of the nervous system. Examplesof physical locations in the brain may include an epileptic focus ordeep brain nucleus, or a physical location elsewhere in the nervoussystem, such as a peripheral ganglion. Alternatively or additionally, insome cases, the physician may hope and expect that the drug will have aparticular effect on a functional circuit of the brain which mayfunctionally connect nerve cells from a variety of locations within thenervous system.

While both the desired effect(s) and the patient's ability to toleratethe drug may depend on the concentration of the drug at the particularphysical locations or in the functional circuits, this concentration isoften not easy to predict just using only data concerning the drug type,the dosage, the class of drug, the method and timing of dosing, and thephysical characteristics of the patient (e.g., sex, height, weight, age,etc.). If the concentration at a location of interest is too low (or toohigh), it may be partially or entirely ineffective in achieving thedesired result. If the concentration of a drug at a location of interestis too high (or perhaps under some circumstances too low), the drug maybe effective to some degree but it nevertheless may not be welltolerated by the patient (e.g., it may be toxic to the patient or maycause the patient to experience one or more undesirable, unpleasant, orquality-of-life-altering side effects).

The effectiveness and the extent to which a patient tolerates a givenmedication also may depend on whether the concentration of the drugremains stable at the location(s) of interest during the time thepatient is intended to experience the benefits believed to be associatedwith the drug. Measuring changes in drug concentration over time in apatient can be challenging. While the systemic concentration of amedication can be measured by assays of serum, such serum assays willnot directly convey the concentration of a given drug at a specificlocation or circuit of interest in the neural tissue or even generallyin the central nervous system.

Moreover, it will be appreciated that a serum assay will only yieldinformation about the concentration of the drug as of the time the serumis sampled, and in order to monitor changes in the concentration overtime, either additional samples will need to be taken and assays run orcertain inferences about how the concentration of the medication willchange over time will have to be made. Also, some drugs have an effectat a location of interest which is not related directly to the serumconcentration. For example, some medications have a long-lasting effectafter a single or several doses, even after the serum concentration hasfallen.

In some circumstances, a driver for providing a patient with additionaldoses of the medication is not related to the serum concentration butinstead to when the physiological effect of the medication ends orsubsides. An example of this is the antiepileptic medication vigabatrin.Vigabatrin increases the levels of the inhibitory neurotransmitter GABAby irreversibly inhibiting an enzyme that catabolizes GABA(gamma-aminobutyric acid transaminase). When GABA levels are high,seizures are inhibited. As the enzyme is naturally replenished in thebrain, GABA levels fall and seizures are more likely to occur. At thistime the medication should be readministered. Thus, in somecircumstances, the optimal timing for doses may be better determined bymonitoring the physiological effect of the medication in the centralnervous system rather than by monitoring the level of the medication inthe serum, as by for example a serum assay.

Therefore, it is desirable to assess information relating to theconcentration of a drug or drugs used in a drug therapy usingphysiological data acquired at or near the location(s) at which the drugis intended to act (either a physical location or a part of a functionalcircuit of the nervous system). Moreover, it is desirable to assess thisinformation frequently enough to determine whether the effectiveness ofthe drug at the locations(s) of interest remains stable or varies duringthe time when the drug is intended to be effective.

Referring again to FIG. 1, an arrow A indicates the function of thecirculatory system, the dashed line B indicates the blood-brain barrier,the wide single-headed arrow C indicates the path of a medication in thecirculatory system up until the blood-brain barrier B is encountered,and the narrow, single-headed arrow D indicates that amount of themedication that successfully crosses the blood-brain barrier and makesit to a location of interest within the area denoted by the brokencircle 119 in FIG. 1.

More specifically, a patient may be subjected to a drug therapy thatincludes the patient receiving a drug systemically (e.g., by ingestingor otherwise taking a pill or receiving an injection in the blood streamother than directly at a location at which the drug is intended to act).A medication that is administered systemically to a patient is conveyedto the brain by the systemic circulation and then must cross theblood-brain barrier (see the broken line B in FIG. 1) to be distributedthroughout the brain by the cerebrovascular circulation.

The actual concentration of the medication at a given location in theneural tissue (e.g., in FIG. 1, a location of interest within the brokencircle 119 is receiving the medication directed to it by thecerebrovascular circulation, which is indicated generally with the arrowD) may vary according to the timing at which doses are taken andaccording to the pharmacokinetics of the medication, which may varyacross individuals and even within an individual over short and longperiods of time. Therefore, an amount of medication that will beavailable to neural tissue at a location of interest is difficult topredict even when the precise dose is known (e.g., assuming the patienttakes her pills when she is supposed to), or even when an assay of theconcentration in the serum is undertaken (e.g., by periodically sendingthe patient's blood to a laboratory for analysis).

Additionally, the pharmacodynamic effects of a given medication at alocation in the neural tissue may vary across and within individuals.Thus, the therapeutic effects and side effects of the medication at agiven dose or serum concentration may vary over time and across patientseven when the treating physician's hope and expectation is that themedication will affect the same location(s) or functional circuit(s) ineach patient.

Moreover, in some cases, the physician may not always appreciate how agiven drug works or at which locations it works more or less effectivelyto achieve a desired result. Ultimately, the physician wants to knowwhat the functional concentration of the medication is at the neuraltissue of interest, that is, whether the medication is having thedesired effect. When the physician has an understanding of this thephysician can adjust the dose in order to achieve the desired effect.

FIG. 1 shows an implantable medical device 100 situated in a structuralmember inserted into the opening formed in the skull by the craniectomy,which structural member is commonly referred to as a ferrule. Theferrule 104 provided with mounting tabs 106 for attaching the ferrule tothe cranium (or skull) 108. The mounting tabs 106 include screw-holes110 or other apertures for receiving bone screws to secure the ferrule104 to the skull 108. The implantable medical device 100 may beconfigurable to monitor physiological activity originating from orsensed from one or more sensing locations in the patient's brain 112.

More particularly, the implantable medical device 100 may be configuredto monitor signals corresponding to field potential measurementsacquired using one or more electrodes placed in or on the brain 112 orto acquire other physiological data corresponding to a state of theneural tissue, such as the level of neurochemicals in the tissue (forinstance, the concentration of neurotransmitters in a particularlocation in the brain), and the degree to which the tissue isoxygenated, etc.

In FIG. 1 the implantable medical device 100 is shown connected to twobrain leads, a cortical strip lead 114 and a deep brain or depth lead116. A proximal end 115 of the cortical strip lead 114 and a proximalend 117 of the depth lead each are connected to the implantable medicaldevice 100 at a lead connector 102. A distal portion 118 of the corticalstrip lead 114 is provided with a strip 120 which is designed to restagainst or adjacent a surface of the patient's brain 112, such as underthe dura mater (not shown in FIG. 1), at a location on the brain 112within the broken circle 119. The distal portion 118 bears fourdisk-shaped electrodes 122, 124, 126, and 128 which are in electricalcommunication with the proximal end 115 of the cortical strip lead 114and with the implantable medical device 100 via conductors in thecortical strip lead 114 (see also FIG. 2A) and via the implantablemedical device connector 102.

The depth lead 116 is implanted at a location in the brain within thebroken circle 129 in FIG. 1. The depth lead 116 is implanted through aburr hole 130 that has been drilled in the skull 108 to allow thesurgeon access to the patient's brain as, for example, in a stereotacticprocedure. Like the cortical strip lead 114, the depth lead 116 isprovided with electrodes at a distal portion 132 thereof. (The ringelectrodes of the depth lead 116 are shown in FIG. 2B.) The electrodesof the depth lead 116 are also in electrical communication with theproximal end 117 of the depth lead 116 and with the implantable medicaldevice 100 via conductors in the depth lead 116 (see also FIG. 2B) andvia the implantable medical device connector 102.

Referring now to FIGS. 2A and 2B, illustrations of the cortical striplead (FIG. 2A) and a deep brain or depth lead (FIG. 2B) are shown. Thefigures are not drawn to scale. The cortical strip lead 114 has aproximal end 115 and a distal portion 118. The distal portion 118 isprovided with a cortical strip 120 and four disk-shaped electrodes 122,124, 126, 128. Each disk-shaped electrode 122, 124, 126, 128 isconfigurable to be in electrical communication through a dedicatedconductor 202, 204, 206, 208 with one of four connection surfaces orcontacts 212, 214, 216, 218 at the proximal end 115 of the lead 114. Theconnection surfaces or contacts 212, 214, 216, 218 can make electricalcontact with the implantable medical device 100 via the connector 102 ofthe implantable medical device with which the proximal contacts 212,214, 216, 218 are configured to mate. The depth lead 116 has a proximalend 117 and a distal portion 132. The distal portion 132 is providedwith four ring electrodes 222, 224, 226, 228. Each ring electrode 222,224, 226, 228 is configurable to be in electrical communication througha dedicated conductor 232, 234, 236, 238 with one of four connectionsurfaces or contacts 242, 244, 246, 248 at the proximal end 117 of thedepth lead 116. The connection surfaces or contacts 242, 244, 246, 248can make electrical contact with the implantable medical device 100 viathe connector 102 of the implantable medical device (with which theproximal contacts 242, 244, 246, 248 are configured to mate). Each ofthe disk-shaped electrodes 122, 124, 126, 128 and the ring electrodes222, 224, 226, 228 may be constructed of a biocompatible, conductivematerial such as platinum or a platinum/iridium alloy.

In addition to or in lieu of one or more electrodes on the leadsdescribed with reference to FIGS. 2A and 2B, the implantable medicaldevice 100 may be used with other sensors or probes (not shown). Suchother sensors or probes may be either hard wired or in wirelesscommunication with the implantable medical device 100 so that the devicemay monitor physiological data other than data acquired using theelectrodes. For example, probes for oximetry and micro/macroelectrodeconfigurations for accomplishing voltammetric measurements relating toneurochemical concentrations may be used to provide other physiologicaldata to the implantable medical device 100. A probe may be used toacquire a signal corresponding to the level of the near-infraredwavelength characteristic of light absorption by oxygenated hemoglobin(HbO2). This signal may be used to estimate a level of neural activity.For instance, the neurovascular coupling system causes vasodilation andincreased cerebral perfusion in response to neural activity, such that,after an initial drop in oxygenated hemoglobin at the onset of increasedneural activity, increased neural activity is then accompanied by anincrease in oxygenated hemoglobin.

Variations of sensors or probes may be implemented using transducers foradditional sensing modalities such as optical infrared spectroscopy. Agiven sensing modality may rely upon active electronics provided in thelead, especially at a distal portion of a lead close to where thephysiological data is being sensed, to acquire physiological data foruse by the implantable medical device. Alternatively, a given sensor maybe associated otherwise locally with active electronics and the sensorinformation acquired may be communicated to the implantable medicaldevice wirelessly.

While the implantable medical device 100 is shown at a particularlocation on the patient's head, it will be appreciated that it may belocated elsewhere. For example, the implantable medical device 100 maybe situated in a hole formed by a craniectomy at another site on theskull, or may be situated in a recession made in the skull, or betweenthe scalp and the skull. In other cases, the implantable medical device100 may be implanted further away from the location at which thephysiological data it monitors originates or is generated. For example,it is known to situate an implantable medical device in the pectoralarea of a patient and then to place the implantable medical device incommunication with the patient's brain using leads that extend from theimplantable medical device through the patient's neck up to the brain,where electrode-bearing lead distal ends can be introduced to one ormore locations on, adjacent to, or in the patient's brain tissue.

In still other circumstances, the implantable medical device may be usedto accomplish one or more of its intended functions, e.g., to monitorphysiological data sensed by one or more sensors, without theimplantable medical device actually being implanted (for instance toperform a short-term test to confirm that the electrodes of a brain leadare in the desired location) or with the implantable medical devicebeing only partially implanted.

In addition to being configurable to monitor physiological data, theimplantable medical device 100 in some embodiments may also beconfigurable to generate and output electrical stimulation whichelectrical stimulation may be delivered to the patient through pathwaysformed, for example, between electrodes on the distal end of a brainlead or between one or more electrodes on the distal end of a brain leadand a conductive housing provided for the implantable medical device100.

An implantable neurostimulation system manufactured under the tradename“RNS SYSTEM” by NeuroPace, Inc. of Mountain View, Calif. is underinvestigation that is configurable to acquire, process, and analyzeelectrographic activity from a patient and to generate and deliverelectrical current stimulation to the patient, for example, in responseto the results of the analysis of the electrographic activity. Morespecifically, this neurostimulation system is configurable tocontinuously monitor and on command record electrographic activitysensed from one or more sensing locations on or adjacent or in apatient's brain. The neurostimulator further may be configured toimplement various analytic tools, in sequence or in combination, thatare intended to detect events of interest when the events occur in themonitored electrographic activity. Whenever an event is detected, theneurostimulator may store one or more records corresponding to theelectrographic activity at the time the event is detected, as well asother information about the event, for example, the time the eventbegan, the length of time the event continued to be detected, the timebetween one event and the next event, etc.

The NeuroPace neurostimulator is being investigated for use inapplications to treat patients who have epilepsy. It can be used witheither or both of electrode-bearing cortical strip leads and depth leadswhere the neurostimulator can be programmed to recognize each electrodeas a part of one or more sensing “channels” and programmed to includeeach electrode as part of a pathway through which electrical current canflow through the patient.

Thus, in the NeuroPace, Inc. RNS System as well as in some embodimentsdescribed herein, the factors a physician considers in determining whereto locate the electrodes of a brain lead include selecting stimulationlocations at which or through which to introduce an electrical currentto the brain as well as selecting locations appropriate to sensingphysiological data that can be monitored by the implantable medicaldevice using the leads. Indeed, it will be appreciated that in anycircumstance in which an element may be used to implement both amonitoring or sensing function and a function intended to modulate theneurological behavior of the patient's brain, the location of theelement will require thoughtful consideration and likely the weighing offactors and prioritizing of various hoped-for outcomes.

In some circumstances, the electrodes may be situated at or near alocation in the brain that is understood to constitute a focus ofepileptiform activity (e.g., an epileptic focus). In othercircumstances, the electrodes may be implanted at a particular nucleusdeep in the brain which is understood to have some connection to theparticular neurological disorder for which the patient is being treated,such as a deep brain nucleus exhibiting pathological behavior in apatient with epilepsy or a movement disorder. Locations for electrodesfor sensing or other sensors of physiological data or for stimulatingareas of the brain can include regions of neural tissue located in thebrain 112, regions of neural tissue located outside the brain, such ascranial or peripheral nerve ganglia, or regions of non-neural tissuesuch as cardiac or muscle tissue.

It will be appreciated that sensing physiological data from one sensinglocation may relate to behavior of a physical location that is remotefrom the sensing location or may relate to the function of a neuralcircuit, the components of which are physically spread out through thenervous system. It further will be appreciated that the desired effectof stimulation at a given stimulation location may not be fully realizedor realized at all at the stimulation location itself, but rather isrealized at a region distant from that location. For example, thedesired effect of stimulating a given location of interest may be tocause excitation (or inhibition) of neurons located remote from thatlocation of interest but which receive excitatory (or inhibitory) neuralprojections from the location of interest. The systems and methodsdisclosed here beneficially may be used when the locations used forsensing physiological data or for delivering a form of neuromodulationtherapy are either directly or indirectly related to the condition beingsensed or the behavior a given therapy is intended to modulate.

Further, it will be appreciated that the implantable medical device maybe configurable to deliver forms of therapy using elements other thanelectrodes, such as via drug-eluting leads or components foradministering optical stimulation.

Referring now to FIG. 3, a block diagram of systems and methodsaccording to embodiments is shown. In these embodiments, the implantablemedical device 100 is an implantable neurostimulator that isconfigurable to generate and output a form of electrical stimulation fordelivery to the patient according to a set of programmable stimulationparameters. The various blocks shown in FIG. 3 (and in any other similardrawing figure included herein) are used for convenience in thediscussion of some of the functions the implantable neurostimulator 100is configurable to undertake. It will be appreciated that the variousfunctions and capabilities of the “modules” or “subsystems” depicted inthe block diagram may be performed by electronic hardware, computersoftware (or firmware) or any combination thereof. The actual divisionof work for each of the various functions may not be well represented bythe blocks shown in the diagram of FIG. 3 and the diagram may notreflect a real-world integration of the functions into a system ormethod according to embodiments.

The implantable medical device 100 is also configurable to acquireinformation relating to physiological data sensed from the patient, andto process and analyze the information.

The acquiring may include selecting which of several channels from whichto accept input. In FIG. 3, a “sensing” module 312 and a “multiplexer”314 are shown in the implantable medical device 100. For example, theimplantable medical device 100 may be configured to receive inputscorresponding to one or more channels of physiological data acquiredfrom the sensors (e.g., electrodes). FIG. 3 shows a“sensing/stimulation” element 340 that is capable of being configuredeither to sense physiological data from or deliver stimulation to thepatient 302, as well as an additional “sensing” element 342 that isdedicated for use in sensing. A sensing/stimulation element 340 maycomprise an electrode that can be configured to sense physiological datafrom a patient (e.g., a field potential measurement corresponding toelectrical activity in the area in which the electrode is implanted) andthat can be configured to deliver an electrical current to the patient(e.g., through a pathway that includes the electrode). A sensing element342 may comprise an electrode for measuring field potential changes inelectrical activity of the brain, or a component or collection ofcomponents configured to sense some other type of physiological data,such as an optical sensor configured to detect wavelengths of infraredlight corresponding to oxygenated and deoxygenated hemoglobin.

In some embodiments, the implantable medical device 100 may beconfigured to acquire information from one or more sensing elements 342that are situated in one or more locations in a patient to measurelevels of a neurochemical. This information may include pH, tissueoxygenation, and/or neurotransmitter levels. During periods of increasedneural activity, energy utilization by neural tissue results inincreased metabolism that lowers extracellular oxygen concentrations andpH. At the same time, chemical messengers are released by neural tissuethat result in vasodilation and an increased supply of nutrients. Thisvasodilation increases blood flow, re-supplying oxygen and clearingcarbon dioxide. Because vasodilation overcompensates for the metaboliceffects, the net result is an increase in oxygen levels and an alkalineshift that occur following increased neuronal activity. Both chemicalchanges are transient and approximately simultaneous, occurring a fewseconds after the electrical activity. Both oxygen and pH levels can bemeasured in the brain using fast-scan cyclic voltammetry. Extracellularoxygen levels can also be measured using optical recording of intrinsicsignals (ORIS). ORIS relies on the differential absorption of oxygenated(Hb02) and deoxygenated hemoglobin (Hbr). At isobestic wavelengths (525,545, 570.5 and 583 nm) Hb02 and Hbr reflect light equally and thus theresulting signal reflects total hemoglobin. Total hemoglobin is directlyproportional to cerebral blood volume and cerebral blood flow giving ameasure of tissue perfusion. At higher wavelengths (605-650 nm), themajority of the signal comes from Hbr since Hbr has a higher absorptioncoefficient than Hb02. Using ORIS may require using light emittingdiodes to illuminate and an isolated photosensitive diode to detect thereflected light. Similar technology has been used in to detect oxygensaturation in cardiac tissue. Alternative technologies for sensingoxygen include quench fluorescence and impedance plethsymography.

Voltammetry can also be used to measure levels of specificneurotransmitters, such as dopamine, adenosine, serotonin, andnorepinephrine or electrochemically active neuropeptides such asoxytocin and vasopressin. Other or additional neurotransmitters,including glutamate and GABA may be measured using methods including butnot limited to fixed potential amperometry at enzyme-linked biosensors.

Either the programmable parameters for configuring the implantablemedical device 100 to identify characteristics in the sensedphysiological data or the programming instructions that control thedevice's central processing unit (and thus its overall operation) orsome combination of both define, at any given time during when thedevice is functioning to monitor physiological data from the patient,which input signals representing which physiological data are connectedto which sensing channels that are configured in the implantable medicaldevice.

A multiplexer function is provided in the implantable medical device 100and is labeled as “multiplexer” 314 in FIG. 3 and also may be referredto herein as “the multiplexer module”. In some embodiments, themultiplexer 314 routes signals coming into the implantable medicaldevice, such as voltages corresponding to sensed physiological data, toamplifiers or other signal processing circuitry, for example, signalprocessing circuitry that forms a part of the functions carried out bythe sensing module 312.

The sensing module 312 is provided in the implantable medical device 100and may be configured to receive signals or other data acquired by theimplantable medical device 100 and process the signals and/or data intoa form that can be used by the other modules of the implantable medicaldevice, such as the detection module 318, the recording module 320, theevent counting/logging module 322 and the control module 326. Thefunctions of the sensing module 312 may include converting an analogsignal to a digital approximation of the signal. The sensing functionsof the implantable medical device 100 may also include amplifying,low-pass filtering, high-pass filtering, bandpass filtering, and/orbandstop filtering of signals. The processing may include such things asdebouncing, conditioning, smoothing, low-pass filtering, or high-passfiltering of a signal indicative of the level of a physiologicalmeasurement. The processing may be undertaken as part of one or more ofthe functions of “sensing” and “detection” indicated by the sensingmodule 312 and detection module 318 in FIG. 3.

The detection module 318 is provided in the implantable medical device100 and is configurable to analyze and evaluate signals or other datacorresponding to physiological data acquired by the implantable medicaldevice. The analyzing may include applying one or more algorithms to theacquired and processed physiological data and, optionally, comparing oneor more results of the algorithms to a value, such as a fixed or dynamicthreshold. The analyzing may be undertaken on physiological data in theform of an EEG signal (e.g., an electrocorticogram (ECoG)) sensed frominside the skull (as opposed to sensed through the skull, as with ascalp electrode), in the form of a different electrophysiologicalwaveform (e.g., a waveform corresponding to changing levels ofneurotransmitter concentration in a time window), or in the form of asensor measurement that is not necessarily acquired as a waveform (e.g.,a temperature or pressure measurement, a tissue oxygenation level, or anaccelerometer reading (to indicate rest or sleep versus movement or anawake state)).

In some embodiments, the analyzing and evaluating includes detectingcertain pathological events, such as a spike or a seizure that isdiscernable in a sample of electrographic activity sensed from thepatient's brain. The analysis may further include identifying half wavesin the sample, evaluating a line length trend and an area trend for thesample, and comparing the results of the analysis to one or more limitsor thresholds.

More particularly, in an embodiment, the implantable medical device 100can be configured to analyze data it acquires corresponding to fieldpotential measurements sensed using electrodes with one or all of threetools, known as the half-wave tool, the line-length tool, and the areatool, each of which is described in more detail below and, for example,in U.S. Pat. No. 7,966,073 issued Jun. 21, 2011 for “DifferentialNeurostimulation Therapy Driven By Physiological Therapy” to Pless etal. U.S. Pat. No. 7,966,073 is incorporated herein by reference in theentirety. The tools may be implemented in a combination of hardware andsoftware, or entirely in one or the other, depending on overall systemrequirements such as power consumption limitations.

By way of example, in some embodiments, where the physiological databeing sensed is a field potential corresponding to an electricalactivity of the patient's brain, each sensing channel of the detectionmodule receives a bipolar signal representative of the difference inelectrical potential between two selectable electrodes. An interface inthe implantable medical device 100 with the sensors (such as anelectrode selector) provides signals corresponding to each pair ofselected electrodes to a sensing front end of the detection module. Thesensing front end amplifies the incoming signal(s), converts the signalfrom analog to digital form, and multiplexes the signals on the sensingchannels.

Preferably, any of the electrodes can be used differently depending on apreferred monitoring configuration. For example, an electrode may remainunused while the detection module is monitoring physiological datasensed by other electrodes such that the unused electrode is notconnectable to a sensing channel with the electrode selector.Alternatively, an electrode may be coupled to either a positive or anegative input of a single sensing channel or an electrode may becoupled to the positive (or negative) inputs of multiple sensingchannels.

A multiplexed input signal representative of all sensing channels thatare active during monitoring may be fed from the sensing front end to adata analyzer. The data analyzer may be a special-purpose digital signalprocessor (DSP) adapted for use in the detection module. Alternatively,a programmable, general purpose DSP may be used in the detection module318.

The half-wave tool, the line-length tool, and the area tool each may becharacterized as a tool for analyzing an EEG. There may be multipleinstances of each of these tools associated implementable in thedetection module, having detection parameters that can be programmedwith different values. Different instances of the tools may beselectable to operate on the data processed through different sensingchannels. The results of the tools may be used alone or in combinationto decide whether an “event” should be deemed to have been “detected” inthe sample of the signal analyzed.

The half-wave tool measures characteristics of an EEG (or ECoG) signalrelated to the dominant frequency content of the signal. In generalterms, a half wave is an interval between a local waveform minimum and alocal waveform maximum; each time a signal “changes directions” (e.g.,from increasing to decreasing or from decreasing to increasing), andsubject to limitations that are set forth further below, a new half waveis identified. The half wave tool, particularly when used on filteredEEG data, can be used to identify the presence of signals in particularfrequency ranges over certain periods of time, such as a frequency rangethat correlates well with a time when a patient is experience seizureactivity. In an embodiment, for example, the analysis performed by thedetection module 318 includes detection of power within a frequencyband, such as from 13 to 30 Hertz, by analyzing half-waves that occur inone or more time windows in a sampled electrographic signal sensed fromthe patient's brain and acquired by the implantable medical device 100.

The line length tool is a simplification of the fractal dimension of awaveform, and reflects how much an EEG signal is varying in a given timewindow.

The area tool is a simplification of the energy of a waveform, andinvolves calculating the area under the curve of a EEG signal within acertain time window.

Specific implementations of each of a half-wave tool, a line length tooland an area tool are described in U.S. Pat. No. 6,810,285 to Pless etal. for “Seizure Sensing and Detection Using an Implantable Device”,issued Oct. 26, 2004. This patent also describes particular applicationsof the tools in a system including an implantable neurostimulator which,among other things, continuously acquires electrographic signals sensedfrom a patient and processes and analyzes the acquired data to monitorfor certain “events” (e.g., a pattern in a certain time window or acertain combination of a pattern and some other characteristic of theacquired data or a condition of the implantable neurostimulator), and toregister a “detection” or “detected event” whenever the event occurs.The detected events may be used in a form of treatment for a patientexperiencing seizures or “ictal” or “epileptiform” activity, such as aform of treatment involving delivering a therapy of electricalstimulation whenever an event is deemed to have been detected by theimplantable neurostimulator. U.S. Pat. No. 6,810,285 is incorporatedherein by reference in the entirety.

Different or additional tools may be used to evaluate EEG waveforms,other electrophysiological waveforms and other sensor data in accordancewith embodiments. For example, an EEG waveform may be analyzed in thefrequency domain by a tool that involves fast Fourier transforms (FFTs).The analysis tools may be used alone or in combination (e.g., in aBoolean combination) to analyze the physiological data sensed from thepatient. A tool or tools may be implemented entirely by the implantablemedical device or in part by the implant and in part by one or moreexternal components. Physiological data acquired by the implantablemedical device 100 may be subjected to more than one tool at the sametime or to one tool followed by another tool.

The analyzing may include comparing a result of an algorithm oralgorithms with one or more thresholds, fixed or dynamic, or othervalues. The results can be logically combined, thresholded, trended, orsubjected to further analyses or processing steps as necessary to detectneurological events or states, or to identify other characteristics inthe acquired physiological data according to embodiments.

In an embodiment, any detection tool or other algorithm for analyzingdata with the detection module 318 easily may be tuned to operate onessentially any kind of source data. It will be apparent that detectionof a pathological event or pathological activity can include thecondition occurring when the output of one of these analysis toolsexceeds or falls below a threshold, such as a programmable parameterrepresenting the threshold between normal physiological variation andpathological neural activity. It also will be apparent that apathological event may be deemed to have been “detected” when acombination of conditions occurs, such as a Boolean AND combination,Boolean OR combination, or other logical combination, or a time sequenceof such conditions occurring such as the output of a first analysis toolexceeding a first threshold followed within one second by the output ofa second analysis tool exceeding a second threshold.

In some embodiments, the detection module 318 is configured to analyzethe acquired physiological data by determining a quantity or a qualityof periodic variation with which the acquired physiological data ischaracterized. This quantity or quality of periodic variation maycomprise one or more of an ultradian, circadian, or circalunarvariation. The quantity or quality of periodic variation may beidentified as a characteristic of a physiological data subjected to aline length tool (e.g., identified based on the variation of line lengthof an electrocorticographic signal averaged over time or a count ofpathological events).

Determining the quantity or quality of the periodic variation mayinvolve one or more of the following analytic approaches: (1)determining a frequency or period of the periodic variation; (2)determining a modulation depth of the periodic variation; (3)determining an autocorrelation of a physiological measurement (e.g.,wherein successive values of the physiological measurement arecorrelated with each other and the degree of correlation is quantifiedin some manner relative to the successive values); (4) determining acorrelation or a coherence between multiple physiological measurements;(5) determining a phase of a periodic variation with respect to a phaseof a different physiological measurement; and (6) determining a phase ofa periodic variation with respect to a time interval such as calendardays, 28-day intervals, a patient's sleep cycle, a patient's medicationschedule, or a patient's menstrual cycle.

The quantity or quality of period variation with which the acquiredphysiological data is characterized may be useful, for example, inassessing whether a drug regimen to which the patient is subjected iseffective or the time or times when the drug regimen is or is noteffective. For example, the effectiveness of a medication may beestimated to be inversely proportional to the autocorrelation of thecount of events at a 28-day time difference. Based on this information,the physician may choose to change the time at which the drug is takenso that the peak concentration corresponds to times when thephysiological data indicates that the drug is less effective, and/orchange the dosage on certain days of the month (such as over a menstrualcycle) during which the physiological data indicates that the drug isless effective or even change the drug entirely.

The implantable medical device 100 further is configurable to storeinformation relating to the sensed physiological data (e.g., waveformsor filtered or processed waveforms), store information relating to oneor more conditions of the neurostimulator at the time the sensedinformation is acquired (e.g., a date/time stamp, whether an amplifierin a sensing channel of the neurostimulator is saturated and, if so, forhow long etc.), or store information relating to the form of stimulationdelivered to the patient, if any (e.g., information with which adelivered stimulation waveform may be identified or recognized,information corresponding to whether a desired amplitude of stimulationwas achieved, etc.).

The storing may be undertaken as part of one or more of the functions of“recording” and “event counting or “event logging” indicated by therecording module 320 and event counting/logging module 322 shown in FIG.3. For example, if the implantable medical device 100 is configured toidentify a characteristic in the physiological data it acquires as an“event” which the neurostimulator “detects”, then a function of theimplantable medical device may be to keep track of how many detectedevents occur over a fixed period of time (e.g., 24-hours) or a variableperiod of time (e.g., during a time when the patient is experiencingsymptoms associated with the neurological disorder for which the patientis being treated).

In this same example, another function of the implantable medical devicemay be to store the sample of acquired physiological data in which each“event” was “detected” (or a digitized or otherwise processedtransformation of the sample), so that, for instance, a physician maylater review the sample by interrogating the information stored on theimplant. If the physiological data includes electrocorticograms sensedby measuring field potential changes at one or more sensing locations inthe patient's brain, then what the implantable medical device recordsmay comprise electrographic records. The running count of the number ofdetected events may be stored in the event counting/logging module 322and the electrocorticogram may be recorded in the recording module 320.

In some embodiments, the implantable medical device 100 is configurableto generate and output a form of stimulation to the patient 302. Thegenerating and output of stimulation may be undertaken as part of one ormore of the functions of “stimulation” indicated by the stimulationmodule 324 shown in FIG. 3. Variations of an implantable device that isconfigured to generate and output electrical stimulation signals aredescribed in U.S. Pat. No. 6,690,974 to Archer et al. for “StimulationSignal Generator for an Implantable Device”, issued Feb. 10, 2004. U.S.Pat. No. 6,690,974 is incorporated by reference herein in the entirety.

In some embodiments, the stimulation generated and output by theimplantable medical device 100 is intended to be a form of therapy tothe patient. In other embodiments, the stimulation generated and outputby the implantable medical device 100 is intended to evoke a responsefrom the patient that can be sensed and/or logged and/or recorded and/oranalyzed by any of the implantable medical device, the implantablemedical device in combination with one or more external components, orby external components exclusively.”

The neurostimulator may be configured to deliver the stimulation to oneor more delivery devices or elements. In the block diagram of FIG. 3,one such delivery element is indicated by the label “stimulationelement” 344. An example of a stimulation element 344 is an electrodeconfigured to form part of a pathway for delivering electrical currentthrough the patient. Another example of a stimulation element 344 is adevice or collection of elements or mechanism configured to dispensecontrolled amounts of a neurochemical substance to the patient. As isthe case with some possibilities for “active” sensing elements, a givenstimulation element 344 may require power or one or more control signalsin order to carry out its intended stimulation function.

When the implantable medical device 100 is configured to generate andoutput a form of stimulation, then the multiplexer module 314 may beconfigured to manage signals comprising or otherwise related to the formof stimulation to control delivery of the stimulation to the patient.For example, the multiplexer module 314 may manage current or voltagewaveforms generated for stimulation or control signals that governrelease of neurochemical substances.

Some possible forms of stimulation are described in more detail hereinand include electrical stimulation as well as optical stimulation andstimulation in the form of the introduction of neurochemicals or drugs.The parameters that determine what stimulation is generated and how thestimulation will be output from the device are generally programmableand correspond to a set of stimulation parameters. FIG. 3 shows onepossible destination for a stimulation output labeled as “stimulationelement” 344. It will be appreciated that when the stimulation is, forexample, pulsatile electrical stimulation, the stimulation element 344may be an electrode or combination of electrodes forming a pathwaythrough which current may flow in the patient. The electrode(s) may beon the distal end of one of the cortical strip lead 114 or the depthlead 116 that are described in connection with FIGS. 1 and 2A and 2B.

In some embodiments, the stimulation module 324 may be configured todeliver stimulation, at least some of the time, in response to theoccurrence of a “detected event” or otherwise when the implantablemedical device 100 identifies a particular characteristic in thephysiological data acquired by the implantable medical device (e.g., asfrom one of the sensing elements 342, such as a drop in level of aneurotransmitter at the location of the sensing element). Moreparticularly, the implantable medical device 100 may be configured todeliver stimulation, for example, in the form of a burst of electricalstimulation through one or more electrodes, whenever the device 100determines that something it has been watching for in the acquiredphysiological data has in fact occurred. In these embodiments, multipleones of the possible functional blocks of the implantable medical device100 may be required to communicate with each other. For example,something that the detection module 318 detects may trigger thestimulation module 324 to generate and output stimulation, and themultiplexer 314 may select which of the available stimulation elements344 are available through which to deliver the stimulation. The eventcounting/logging module 322 may store one or more values correspondingto the occurrence of the event or identified characteristic of thephysiological data and the nature of the stimulation delivered inresponse to that occurrence, and whether the implant was able to deliverwhat it was programmed to deliver or something less than that. Therecording module 320 may record what the sensing element(s) 340 sensedbefore, during and after the occurrence of the event or identifiedcharacteristic that resulted in the generation and output of thestimulation, and the event counting/logging module 322 and the controlmodule 326 may store one or more data items that correspond to the factthat the event was detected or the characteristic was identified,including the date and time when the event was detected or thecharacteristic was identified. In other embodiments, the stimulationmodule 324 may be configured to deliver stimulation as a therapy attimes that are not necessarily related to what the implantable medicaldevice determines are events or identified characteristics, but ratheraccording to a schedule or continuously or in reaction to some otherbehavior or command (e.g., a request by the patient or the patient'sphysician to deliver stimulation to the patient). In still otherembodiments, the stimulation module 324 may be configurable to deliverstimulation not as a therapy but rather to evoke a response from thepatient, for example, in assessing the effectiveness of a drug regimenor for a purpose of testing the neurostimulation, detection or otherfunctions of the implantable medical device 100.

The implantable medical device 100 also is configurable to communicateunidirectionally or bidirectionally with one or more externalcomponents, for example, via a wireless communication link. For example,a selectable part-time wireless link to external components may berealized with inductive telemetry (short range or long range) using atelemetry coil or other transceiver part or antenna provided in theimplantable medical device. Alternatively or additionally, communicationbetween the implantable medical device 100 may be establish using magnetfields or interruptions in magnetic fields with a magnetic sensor (e.g.,a reed switch or a GMR sensor) provided in the implantable medicaldevice. Some of the external components may be considered “host” devicesinsofar as an external component can be used to control the implantablemedical device 100, for instance, by transmitting new programmableparameters which parameters will govern the generation and output ofelectrical stimulation from the implantable medical device 100, or bycausing data such as electrographic records stored in the implantablemedical device to be uploaded to the external component. A “host device”may encompass functions carried out by both external and implantablecomponents of a medical device system.

Embodiments of the systems and methods can include multiple ones of eachpossible type of external component or may be configured forcommunication with only a selected subset of all of the possibleexternal components. For example, a given implantable medical device 100may be configured for communication with any inductive wand, magnet, orphysician's programmer but only one patient remote monitor, or with aset of physician programmers under the possession and control ofphysicians in a particular practice.

The operations and functions of the implantable medical device 100 arecontrolled, in whole or in part and most of the time or some of thetime, by a control module 326 labeled as “control” in the block diagramof FIG. 3. The control module may include the functions of controllingthe sensing, multiplexing, detection, event counting/logging, recording,and stimulation as well as managing use of power (e.g., from a primarycell or rechargeable battery) and communicating between the implant andone or more external components whenever the implant is called upon todo so. For example, the control module 326 may determine whether andwhen a given algorithm is executed to govern detection of events orother identification of characteristics in the acquired physiologicaldata. Similarly, the control module 326 may determine whether and when aform of stimulation is to be generated and output by the stimulationmodule 324, if the neurostimulator 100 is configured to generate andoutput any stimulation for therapy, evoking responses, testing a systemconfiguration, or otherwise.

The external components with which the implantable medical device 100 isconfigurable to communicate may include a programmer 362 which, once acommunication link is established with the implantable medical device,may be used to manually control the operation of the neurostimulator aswell as to transmit information to or receive information from theneurostimulator. For example, the programmer 362 can be used to choosevalues for and set parameters in the implantable medical device in orderto adapt the function of the neurostimulator to meet the patient'sneeds. The programmer 362 also can be used to upload or receive data(including but not limited to whatever data have been stored on theneurostimulator relating to the acquired physiological data, the resultsof analyzing the physiological data, and one or more conditions of theneurostimulator at the time the sensed information is acquired). Theprogrammer 362 further can be used to download or transmit program codeor other information from the programmer to the implantable medicaldevice, or to command the implantable medical device to perform specificactions or to change modes as desired by a physician operating theprogrammer. To facilitate these functions, the programmer 362 is adaptedto receive input from a physician (e.g., from a touch screen or keyboardon a laptop or tablet computer) and to provide outputs to the physician(e.g., in the form of an interactive graphical user interface providedon a laptop or tablet computer).

The external components with which the implantable medical device 100 isconfigurable to communicate may also include a patient remote monitor362 or other device intended to be reserved for use primarily by thepatient in whom the implantable medical device is implanted or thepatient's caregiver. The patient remote monitor 362 may be configured toallow the patient to establish communication with the implantablemedical device in order to upload data from the implantable medicaldevice to a network (e.g., via a telephone line or broadbandcommunication scheme), where the data eventually may be stored in adatabase or maintained using a data management system 360.

The external components with which the implantable medical device 100 isconfigurable to communicate may also include an inductive wand 364 whichmay be necessary to establish the wireless communication link betweenthe implantable medical device 100 and the programmer or remote monitor362.

An external component may include or comprise a website interfaceelement that enables a user of the website to access one or more databases in which information obtained from or otherwise concerning theimplantable medical device 100 is maintained. The website interface mayinclude a graphical user interface for interaction between aphysician-user or other user with the data base(s).

One or more external components with which the implantable medicaldevice 100 can communicate or on which data from the implantable medicaldevice can be stored may be used to display information to a user and,in some circumstances, allow a user to interact with the data in variousways. For example, the programmer or remote monitor 362 may have both adisplay and a graphical user interface with which a user can interactwith data obtained from or about the implantable medical device, and thedata management system 360 may be associated with one or more websiteswith which a user can interact with data obtained from or about theimplantable medical device as well as with data obtained from or aboutother implantable medical devices or other data (e.g., data aboutpatient populations).

In some embodiments, data manipulated by a user via a graphical userinterface or the like may be saved locally and/or “posted” to one ormore data bases of the data management system 360. In still otherembodiments, a user may be able to use a graphical user interface toretrieve data from the data management system 360, such as datapreviously acquired from the same neurostimulator via externalcomponents, and display these data to a user and/or allow the user tomanipulate these data.

A user may use one or more external components or an element or featureof an external component (such as an interactive website or an inputscreen), to associate with the patient data about one or more drugregimens to which the patient having the implanted neurostimulator 100is subjected. For example, the physician may be prompted to input dataon a display or a website page concerning the types of medication apatient is receiving, the dose of each medication, the time each dose isintended to be taken, and the level of medication the patient isintended to receive, for example, each day. Alternatively oradditionally, the physician may be prompted to input data on a displayor website page concerning changes made in drug regimens to which thepatient is subjected, for example data concerning dose increase, dosedecrease, addition of a medication, discontinuation of a medication, orchange in dose scheduling.

Alternatively or additionally, the patient may be prompted to input datawhenever he or she takes a medication. (This information could also beprovided by a patient action such as opening the pill bottle orinverting the pill bottle or accessing the pill from some type ofmedication dispensing device.) The information input by the users may bestored on one or more external components, used in real time by externalcomponents while a communication link between the external component andthe implantable medical device is established, or delivered to theimplantable medical device for use by the neurostimulator in adjusting,for example, (1) the parameters that determine what characteristics theneurostimulator identifies in the physiological data it acquires or (2)the parameters that determine what form of stimulation is generated andoutput from the neurostimulator and (3) the parameters that determineunder what conditions (e.g., when) the stimulation is output fordelivery to the patient.

The data concerning a patient's drug regimen(s) may be used inalgorithms executed in one or more external components, the implantablemedical device, or some combination of these in assessing such things aswhether a drug regimen is effective or well-tolerated by a patient and,if not, whether a parameter associated with a drug regimen (e.g., typeof drug, class of drug, dose of drug, method of delivery of the drug, ortiming of delivery of the drug) ought to be varied in an attempt toimprove the therapeutic result for the patient. Alternatively oradditionally, the data concerning the patient's drug regimen(s) may beused in calculations to assess such things as whether one or moreparameters that control the functions of the implantable medical deviceshould be adjusted in an effort to improve the patient's overallresponse to therapy (e.g., a therapy comprising a drug regimen andbursts of electrical stimulation (as are described in more detailbelow)), such as a reduction in the rate of clinically evident seizuresin a patient who has epilepsy.

Referring now to FIGS. 4A and 4B, one example of a type of physiologicaldata that may be acquired with the implantable medical device 100 isdescribed. An electrographic signal 410 corresponds to a field potentialmeasured at one electrode or a field potential difference measuredbetween two or more electrodes (including at least one electrode that isconfigured as a sensing element 342 or a sensing/stimulation element340) over a period of time. The electrographic signal 410 evidences asegment of pathological activity 420 which corresponds to activity thatis characterized by a higher amplitude than the activity that precedesit in the preceding portion 422 of the electrographic signal 410.

For a given instance of the pathological activity 420, after a time thepathological activity may be defined as corresponding to an “event”which it is desirable to log as having been “detected” in theimplantable medical device 100. For example, the detection module 318 ofthe implantable medical device may be programmed with a set of detectionparameters that are meant to cause the implantable medical device torecognize the pathological activity 420 whenever it occurs to store theportion of the signal that evidences the pathological activity 420 inthe recording module 320, and to store one or more data items in theevent counting/logging module 322 whenever the pathological activity 420occurs in the patient.

The pathological activity 420 may be defined, in part, in theimplantable medical device 100 with an “event detected” marker 424(which may correspond to a date and time at which a given occurrence ofthe pathological activity 420 is first recognized (or “detected”) by theimplantable medical device) and to an “end-of-event-detected” marker 426(which may correspond to the time at which the given occurrence of thepathological activity 420 is no longer recognized (or no longer“detected”) by the implantable medical device). The pathologicalactivity 420 may be defined in part as a “duration-of-a-detected-event”428 in terms of the time that elapses between the event detected marker424 and the end-of-event detected marker 426.

It will be appreciated that, in some embodiments, the time at which theimplantable medical device recognizes that a given instance ofpathological activity 420 constitutes the beginning and ending of anevent and, hence, the duration of the event 428, will depend in part onthe rate at which the physiological data (here, the electrographicsignal) is being sampled and/or processed.

FIG. 4B depicts another example of a signal acquired by the implantablemedical device 100 corresponding to electrographic activity of apatient's brain. The pathological activity 420 is recognized and markedwith an “event detected” marker 424 and an “end-of-event-detectedmarker” 426. A “duration-of-detected-event” 428 is defined as theelapsed time between the “event detected” marker 424 and the“end-of-event-detected” marker 426. In FIG. 4B, at some time during the“detected event”, electrical stimulation is delivered to the patient.The period of time over which the electrical stimulation is delivered tothe patient corresponds to the “stimulation delivered” time 430 shown onFIG. 4B.

Referring now to FIGS. 5A-5C, waveforms are illustrated that correspondto forms of electrical stimulation that may be delivered to a patientthrough one or more stimulation pathways including one or morestimulation elements 344 or sensing/stimulation elements 342. FIGS.5A-5C relate to a pulsatile form of electrical stimulation. Thestimulation may be generated by the implantable medical device 100configured as a neurostimulator by various means, including, forexample, using current-controlled or voltage-controlled stimulationpulses. In FIG. 5A, three stimulation pulses 510 are shown. Eachstimulation pulse 510 is characterized by a leading phase 512 and atrailing phase 514. Each of the leading phase 512 and the trailing phase514 is further characterized by a phase width 516. In the example shownin FIG. 5A, the leading phase 512 is positive-going and the trailingphase 514 is equal but opposite to the leading phase 514 and thereforeis negative-going. The phase width 516 of each phase is the same.

Each phase is characterized by an amplitude 518. The amplitude 518 ofeach phase 510 may be measurable in volts (voltage), for example in arange from +/−0.05 V to +/−12 V, or amperes (current), for example in arange from +/−0.01 mA to 15 mA. If the amplitude of each of the leadingphase 512 and the trailing phase 514 of a pulse 510 are the same, thenthe entire pulse 510 may be referred to simply as having that amplitude518.

The leading phase 512 and the trailing phase 514 of a pulse 510 need notbe symmetrical as shown in FIG. 5A, however, it typically is a designgoal or criterion to keep the total charge delivered in the leadingphase 512 of a pulse 510 roughly equal to the total charge delivered inthe trailing phase 514 of the pulse in order to balance the charge atthe interface between the stimulation element 344 (e.g., an electrodeused to deliver stimulation) and the patient (e.g., the neural tissue atwhich the stimulation electrode is situated). Charge-balancing may beaccomplished by manipulating the amplitude 518 and phase width 516parameters of each pulse 510. For example, a pulse 510 may be providedwith a leading phase 512 with the same amplitude 518 and phase width 516as the amplitude and phase width that characterize the associatedtrailing phase, or different but balanced amplitudes and phase widthscan be used for each of the leading phase 512 and trailing phase 514.Further, it may be desirable to limit the charge delivered per phase to25 microcoulombs per square centimeter of stimulation element 344surface area (e.g., electrode surface area when the stimulation element344 is an electrode). Charge-balancing is believed to mitigate againstthe risk that any irreversible electrochemical reactions will occur dueto a build up of charge at, for example, an electrode-to-tissueinterface.

Typical values for the phase width 516 of a pulse 510 are selected fromthe range 40 to 1000 microseconds. However, longer phase widths 516 suchas 0.5 sec, or waveforms that are not charge-balanced, can be used inapplications such as electrical field stimulation or when stimulation isdelivered from outside the scalp, where reversibility of electrochemicalreactions is not essential or as much of a concern.

Each pulse 510 is further characterized by an inter-phase interval 520.The inter-phase interval 520 may be of zero duration, or may be ofnon-zero duration such as 100 microseconds which is believed to increasethe likelihood that a pulse 510 will cause an action potential to occurin any given neuron.

A pulse 510 may be delivered singly, for example, for a given instanceof an electrical stimulation therapy. Alternatively, a series of pulses510 may be delivered in a repeating pattern that comprises a regular orirregular pattern. The duration elapsed between pulses is theinter-pulse interval 524; the inter-pulse interval 524 is inverselyrelated to the frequency of stimulation. The frequency may, for example,be selected from the range 1 to 333 Hz. An instance of delivery ofpulses 510, whether singly or in a series, or in one or more bursts(described below) or otherwise, may be described as delivery of a“stimulation waveform.”

The pulse phase configurations (e.g., amplitude 518 and phase width516), the inter-phase interval 520, and sometimes the inter-pulseinterval 524 (the inverse of which corresponds to the frequency withwhich a set of pulses are being delivered) each may be referred to a“pulse parameter” or collectively as “pulse parameters.”

Referring now to FIG. 5B, the top graph shows a stimulation waveform 530comprising a first burst of electrical stimulation 532 and a secondburst of electrical stimulation 534. The first burst 532 is identical tothe second burst 534 in that each burst is comprised of three pulses510. A burst of electrical stimulation 530 may be defined by one or moreburst parameters, including, for example, the number of pulses 510 perburst (in this example, each burst 532, 534 has three pulses 510), and aburst duration 536, which may for example be selected from the range 0.1sec to 10 minutes. As was the case with the pulses 510 described inconnection with FIG. 5A, a given instance of a burst 530 may bedelivered singly or in one or more sets. In the example shown in the topgraph of FIG. 5B, the bursts are delivered in a set of two, namely, thefirst burst 532 is delivered and followed by the second burst 534. If,as here, a set of more than one burst is delivered as a stimulationwaveform, then there may be an interval between each burst. Moreparticularly, the inter-burst interval 539 defines the time that theneurostimulator will allow to elapse between bursts, which may forexample be selected from the range 0.1 sec to 10 minutes.

It will be appreciated that in addition to delivering a singlestimulation waveform, more than one stimulation waveforms can bedelivered through different stimulation pathways (e.g., formed usingmore than one sensing/stimulation element 340 or stimulation element344). In FIG. 5B, for example, the top waveform 530, which comprises afirst burst 532 of three pulses 510 and a second burst 534 of threepulses 510 may be delivered to a stimulation element 344 or stimulationelements 344 located at a left side of the patient's brain.Simultaneously, a stimulation waveform 540, which is shown identical tothe stimulation waveform 530 delivered to the left side of the patient'sbrain (but which may also be a different waveform) may be delivered to aright side of the patient's brain using one or more differentstimulation elements 344 different from those that are used to deliverthe left brain stimulation waveform 530. Optionally, and as in the caseof the left brain stimulation waveform 530 and the right brainstimulation waveform 540 shown in FIG. 5B, delivery of the right brainstimulation waveform 540 may be delayed for a time after delivery of theleft brain stimulation waveform 530 begins (or vice versa). Such adelivery delay is illustrated and denoted as a “phase delay” 546 betweenthe top graph (left brain stimulation waveform 530) and the bottom graph(right brain stimulation waveform 540) of FIG. 5B. Thus, the parametersdefining or relating to bursts may include the duration of a burst, thenumber of bursts in a set (or the number of bursts delivered in a givenstimulation waveform) and the inter-burst interval.

It will be apparent that an implantable medical device 100 configured asa neurostimulator can be programmed to deliver one or more of thestimulation waveforms described here in response to “detected events” orother characteristics identified in physiological data acquired by theimplantable medical device, such as acquired electrographic activityfrom the patient's brain. For example, the implantable medical device100 may be configured to deliver one or more stimulation waveforms,comprising, for example, a burst 532 of pulses 510 in response to adetected event that represents an instance of an epileptic discharge(e.g., a period of abnormal neural firing characterized by propertiessuch as increased synchrony between neurons) sensed at or near alocation in the patient's brain where one or more sensing elements 342or sensing/stimulation elements 344 have been situated. Alternatively oradditionally, the implantable medical device 100 may be configured todeliver one or more stimulation waveforms to the patient continuously oraccording to a duty cycle (e.g., a duty cycle which dictates whenstimulation waveforms may be delivered and when stimulation waveformsmay not be delivered).

According to some embodiments, any or all of the parameters governing agiven instance of a stimulation waveform such as the amplitude 518 pulseparameter or a burst duration 536 burst parameter can be configured tobe programmable by a user (e.g., a physician using one of the externalcomponents, such as programmer 362) and/or adjustable by the controlmodule 326 of the implantable medical device 100 and/or one or more ofthe external components (e.g., automatically by the implantable medicaldevice, for instance, in a closed-loop feedback circuit implemented bythe implantable medical device).

If the implantable medical device 100 generates and outputs electricalstimulation pulses 510 and/or bursts 532, 534 according to a duty cycle,the electrical stimulation may be defined in part by an “on” cycle 560,in which the neurostimulator is delivering one or more stimulationwaveforms including at least one pulse 510 and an “off” cycle 562, inwhich the neurostimulator is not delivering any pulses 510.

The neurostimulator can be further configured so that a givenstimulation waveform is characterized by pulses that start out beingdelivered at a first amplitude and then gradually increase in amplitudeto a maximum amplitude. Similarly, a given stimulation waveform may becharacterized by pulses that gradually decrease in amplitude towards theend of the period over which the stimulation waveform is delivered. Theset of stimulation waveforms 570 shown in FIG. 5C illustrate both a“ramp up” 564 period for a burst or set of bursts 570 and a “ramp down”period 566 for a burst or set of bursts. The “ramp up” and/or “rampdown” periods may be beneficially applied when there is an actual orperceived risk that a less gradual increase or decrease in stimulationdelivered to a patient will cause the patient to experience discomfortor other unpleasant or undesirable side effects of the stimulation.

While the stimulation waveforms described in reference to FIGS. 5A-5Care pulsatile stimulation waveforms, the implantable medical device 100when configured as a neurostimulator may be programmed to generate andoutput other electrical stimulation waveforms such as sine waves (ordigital approximations of sine waves) or near-DC stimulation, or squarewaves of relatively long durations. Some of these other forms ofelectrical stimulation waveforms are described in U.S. Pat. No.6,690,974, previously incorporated by reference herein. Further, asmentioned elsewhere herein, a given instance of stimulation may take theform of some other signal that is intended to modulate the activity ofneurons in the area of or included in a functional circuit at which oneor more stimulation elements 344 (or sensing/stimulation elements 340)are located in the patient's central nervous system. Such other signalmay comprise optical stimulation. Similarly, the form of stimulation maycomprise delivery of a drug (or a signal generated and output by theimplantable medical device that commands or otherwise results indelivery of a drug from, for example, an implanted or partiallyimplanted drug delivery device).

Referring now to FIG. 6, a system and method is described for using animplantable medical device 100 for assessing the effectiveness of anexisting drug regimen to which a patient is subjected. Alternatively,the described system and method may be used for assessing a patient'sresponse to a change to one or more parameters that define a particulardrug regimen, so that a physician may assess whether the change tends toimprove the effectiveness of the drug regimen insofar as concerns theneurological disorder the drug regimen is being used to treat. Asmentioned elsewhere herein, parameters associated with a drug regimenmay include which drugs a patient is receiving (or is intended toreceive), a type of each drug (e.g., levetiracetam), a class of drug(e.g., generally, an “antiepileptic drug” (AED), or, more specifically,a “sodium-channel blocker”), the dose of drug (e.g., in milligrams), amethod of delivery of the drug (e.g., in pill form for oral ingestion bythe patient, or suspended in a liquid for fluid injection using a needleor an implanted, or partially implanted drug delivery device), or atiming for the delivery of the drug (e.g., twice a day, at certain timesof the day (such as before bed), when a symptom of the disordermanifests, (e.g., the patient believes he or she is having a seizure orthe patient experiences a symptom of a movement disorder (for instance,tremor)).

An implantable medical device 100 such as the implantable medical deviceand/or implantable neurostimulator 100 described with reference to FIGS.1-5 herein, may be programmed by a physician to acquire physiologicaldata from one or more sensing locations in a patient, and to process,analyze and evaluate the acquired physiological data in an effort todetermine whether the acquired physiological data evidences what theimplantable medical device 100 (e.g., via a detection module 318) isprogrammed to recognize as a “detected event” or another identifiedcharacteristic in the physiological data. An example of a “detectedevent” may correspond to a segment of an acquired electrographic signalfor which the criteria associated with one or more analysis tools (suchas a half-wave tool and/or a line length tool) have been satisfied andmay include the segment of the signal itself as well as conditions ofthe device at the time the detected event occurred, such as an “eventdetected” time 424 and a “end-of-event-detected” time 426 and/or and a“duration-of-detected-event” 428. An example of an identifiedcharacteristic may be when the level (or concentration) of aneurotransmitter being sensed by a sensing element 342 falls below acertain threshold level or trends too low or the like.

If a user (e.g., a physician) has determined that a particular type ofdetected event or particular types of detected events or type of otheridentified characteristic can be correlated to whether a given drugregimen either is effective in achieving a desired therapeutic result oris well-tolerated by the patient, then the physician can configure theimplantable medical device 100 to monitor a variable that reflects thecorrelation. For example, if the effectiveness of drug regimen isunderstood to be correlated to the number of times the electrographicactivity sensed from certain locations in the patient's brain evidencesseizure activity, and the implantable medical device 100 is configuredto recognize such seizure activity and register it as a “detectedevent,” then the number of detected events occurring in the signal(s)acquired by the implantable medical device 100 over a particular periodof time (e.g., 24 hours), may provide a measure of how effective thedrug regimen is for the particular patient. For example, if the count ofdetected events exceeds a certain threshold, the physician may infer orconclude that the drug regimen should be changed in some respect (e.g.,by adding or removing a particular drug from the mix or changing thedosage of a drug, etc.) in order to improve the therapeutic effect ofthe drug regimen.

It will be appreciated that the count of detected events is just oneexample of a metric the implantable medical device 100 may be configuredto track and/or store and/or record (for example, with the sensingmodule 312, the detection module 318, the event counting/logging module322, and the recording module 320 each under the control of the controlmodule 326), in order to facilitate an assessment of the effectiveness(or the patient's tolerance of) a drug regimen, either by a physician orby the implantable medical device 100 or an external component operatingalone or in conjunction with the implantable medical device 100 and/orthe physician. Other metrics may include duration of detected events,rate of detections over time, changes in power in specific frequencybands, pH shifts, tissue oxygenation, neurotransmitter levels, or evokedpotential “EP” amplitude.

It will be appreciated that in some circumstances, it may be appropriateto configure the implantable medical device 100 to acquire and identifyone or more baselines corresponding to a condition of the patient beforestarting the patient on a particular drug regimen or before changing oneor more parameters of a drug regimen.

Referring again to FIG. 6, a physician may configure the implantablemedical device 100 (e.g., an implantable medical device comprising aneurostimulator) (at the flow chart block 610) to acquire physiologicaldata from one or more sensing elements 342 with which the implantablemedical device is in operable communication, where the physiologicaldata corresponds to electrographic activity or neurochemical levelsindicative of the concentration of a medication or medications at ornear a location of interest in the patient's neural tissue.

Examples of brain electrographic activity that may correlate to theconcentration of a medication may include an electrographic pattern orwaveform (e.g., spikes) that the physician has reason to believeconstitute pathological activity or otherwise abnormal activity. Forexample, spikes occurring in a monitored electrographic signal may beunderstood to be associated with epileptiform activity (e.g., abnormalneural firing characterized by properties such as increased synchronybetween neurons), clinical seizure activity, or electrographic seizures.Examples of neurochemical levels indicative of the concentration of alevel of medication include a measurement acquired from a voltammetrysensor (such as configured for cyclic voltammetry). For example, sincelow levels of serotonin may be associated with major depressive disorder(MDD), low serotonin levels measured using cyclic voltammetry may beunderstood to be associated with MDD, and therefore serotonin levelsmeasured using cyclic voltammetry may be understood to be associatedwith effectiveness of medications such as selective serotonin reuptakeinhibitors that act by increasing serotonin levels in MDD.

After the implantable medical device 100 has been configured and,optionally, any relevant baselines have been measured and captured forlater comparison to the information, and the implantable medical device100 acquires, processes, and analyzes at block 620 of the flow chart ofFIG. 6, the patient in whom the implantable medical device is implantedis subjected to a medication change. The medication change may involve,for example, starting the patient on a drug regimen or adjusting aparameter characterizing an existing drug regimen, such as adding a newdrug, changing the dosage of a drug, maintaining the same total dosagebut instructing the patient to ingest a pill more frequently or atdifferent times of the day, or when the patient thinks he isexperiencing a condition or symptom of the disorder for which he isbeing treated, etc.

Subsequent to the medication change, at block 630 of the flow chart ofFIG. 6, an assessment of the effectiveness of the drug regimen followingthe medication change is undertaken. The assessment may be undertakenusing physiological data obtained from the implantable medical device100. The assessment may result in one or more of a display of data to aphysician concerning the drug regimen, a recommendation to a physicianconcerning the drug regimen (such as to adjust or further adjust aparameter of the drug regimen), or an automatic adjustment of aparameter by the implantable medical device 100 that initiates a changeto the drug regimen (e.g., by causing a drug to be delivered from animplanted drug delivery device (which may or may not comprise theimplantable medical device 100 used in undertaking the assessment)and/or a change to another therapy to which the patient may be subjected(e.g., an electrical stimulation therapy delivered from the implantablemedical device 100 or a different implantable medical device).

In some embodiments, the assessment of the effectiveness of the drugregimen following the medication change includes displaying to thephysician on an external component a graphical or tabular representationof the rate of occurrence of each “detected event” the implantablemedical device 100 is configured to recognize and track both after themedication change was made. The assessment further may includedisplaying to the physician a baseline rate of occurrence for eachdetected event to which the rate of occurrence after the medicationchange may be compared and contrasted, so as to, for example, inform thephysician's determination of whether to change a parameter of the drugregimen or a parameter defining or controlling another form ofstimulation intended to modulate the patient's neural activity. Theassessment additionally or alternatively may include displaying to aphysician a target rate of occurrence for each detected event which thephysician also may use for comparison and contrasting purposes.

In some embodiments and as indicated by the block 640 in the flow chartof FIG. 6, after the medication change, the assessment of theeffectiveness of the medication change may include determining whether atarget has or has not been met, and if the target has not been met,initiating a further change to the medication as indicated by the block650 in FIG. 6. If and when the target is met, a decision to maintain thecurrent drug regimen may be made, as indicated by the block 660 in FIG.6.

Embodiments of the method illustrated in the flow chart of FIG. 6 may bedescribed with reference to the following example. Before a medicationchange is introduced to the patient, the implantable medical device 100may be commanded to acquire and calculate a baseline rate of occurrenceof spikes (for example, a count of how many spikes occur in anelectrographic signal continuously monitored from the patient over aperiod of 24 hours). A “spike” may be defined for the implantablemedical device 100 as a feature that occurs in a monitoredelectrographic signal sensed from a location in the patient's brain thatis believed to be a focus for epileptiform or ictal or seizure activity.The implantable medical device 100 may be configured so that, forexample, the detection module 318 will recognize a “spike” in theacquired physiological data whenever a segment of a signal beingacquired is characterized by a certain amplitude for no more than acertain period of time. The implantable medical device 100 further maybe configured to keep track of each time a spike occurs by storingand/or updating one or more data items in the event counting/loggingmodule 322.

Merely for the purposes of illustrating this example, the baseline ratebefore the medication change may be 100 spikes per day. Alternatively,before a medication change is introduced to the patient, the physicianmay have selected a target rate for the number of spikes per day thatrepresents a number of spikes per day that the physician would like notto be exceeded in the patient. For example, the physician's goal may beto keep the number of spikes the patient experiences per day below 100.

Before the medication change, the implantable medical device 100 may beconfigured to recognize as a “detected event” each occurrence of a spikeand to keep track of the rate at which the spikes occur.

After the medication change, the implantable medical device 100 maydetermine that the number of spikes that occur in the first 24-hourperiod following the medication change is unchanged from the baseline orwell below the not-to-exceed target of 100 spikes per day. These resultsmay be uploaded from the implantable medical device 100 and displayed ina meaningful way that is also easy to understand, for example, on adisplay of a laptop computer (e.g., a programmer 362) or via a websitethat interfaces with the programmer 362 or with a data base such as adata base contained within a data management system 360. The results maybe displayed to the physician together with the baseline data and/or thetarget rate so that the physician can readily appreciate whether a goalor goals of the drug regimen have been met (i.e., whether the drugregimen is seems to be effective, at least for the past 24-hour period).

Alternatively, after the medication change, the implantable medicaldevice 100 may determine that the number of spikes that occur in thefirst 24-hour period is fewer than the number of spikes that occurred inthe baseline. Or the post-medication rate of spike occurrence may beonly slightly below the not-to-exceed target of 100 spikes per day. Ineither or both of these cases, the physician (or the implantable medicaldevice 100 functioning autonomously and automatically) may furtherchange a parameter of the drug regimen (e.g., increase a dose) and thenre-assess whether that additional change further reduces the rate atwhich spikes occur in the patient in the next 24-hour period.

In other circumstances, after a medication change, the implantablemedical device 100 may report that the rate of occurrence of spikes inthe next 24-hour period either exceeds the rate of occurrence of spikesin the baseline period or exceeds the not-to-exceed rate associated witha target. In this case, the physician (or the implantable medical device100) may also further change a parameter of the drug regimen and thenre-assess whether that additional change improves the effectiveness ofthe drug regimen by bringing down the rate of occurrences of spikes.

A display over which the physician may view and appreciate the resultsof a given assessment of the effectiveness of a drug according toembodiments may include a feature such as a graphical user interfacethat allows the physician to initiate additional changes to the drugregimen. For example, upon comparing and contrasting the results of ametric obtained from the implantable medical device 100 following amedication change with a like metric in a baseline or associated with atarget, the physician may decide to make a change to one or more of theparameters defining the patient's drug regimen and the graphical userinterface may enable the physician to input the change.

Data about the patient's drug regimens and changes made thereto may bestored on one or more of the external components, such as the programmer362 or in a database of the data management system 360, and/or on theimplantable medical device 100 for later uses associated with treatingthe patient and other purposes related to patient care. In someembodiments, commands input to the programmer 362 to change a medicationor some other parameter defining a drug regimen may be communicated toone or more drug-delivery devices implanted in the patient in order toeffectuate the commanded change.

It will be appreciated that, based on the capabilities and features ofthe implantable medical device 100, the implantable medical device 100may be configured to provide many different metrics that vary in typeand kind that can be used beneficially with embodiments in order toassess the effectiveness of a given drug regimen. For example, in apatient being treated for epilepsy, a metric may be the rate ofoccurrence of one or more abnormal electrographic patterns of interestor waveforms of interest (such as a waveform other than a “spike”),where a given drug regimen would be deemed to be more effective when therate of occurrence of such patterns or waveforms of interest decreaseover time as compared to a baseline or target rate. For example, theabnormal electrographic pattern of interest may be an electrographicseizure that lasts at least five seconds, and a not-to-exceed target maybe not to exceed 10 of these at-least-five-second seizures per day. Orthe abnormal electrographic pattern of interest may be an electrographicseizure that lasts at least 90 seconds, and the target for the patientto experience no more than one seizure per week that lasts at least 90seconds.

Put another way, at effective overall concentrations of medication,there should be fewer occurrences of detections of the abnormalelectrographic patterns and waveforms by the implantable medical device100 and there also should be fewer occurrences of seizure activity thatthe patient recognizes or notices. (In epilepsy, intracranial sensingelectrodes may sense epileptiform activity from the brain, for example,even while the patient does not appreciate that he or she is having aseizure: there is a distinction between electrographic seizures andepileptiform activity, on the one hand, and “clinical seizures” on theother. In other words, a patient may experience an electrographicseizure without also experiencing a clinical seizure and the patient maynot appreciate that the electrographic seizure is occurring.) It isnoted that seizures that the patient recognizes or notices are oftenrelatively rare, such as one per week, and the rate and incidence ofthese seizures is often highly variable over time. Further, reporting ofsuch seizures by patients is often erroneous or missing. This means thatestimates of the effectiveness of medication based only on the reductionof clinically or visibly observable symptoms, such as seizures that thepatient recognizes or notices, are often highly uncertain. An advantageof the embodiments is that measurements, such as counts of detectedevents determined by an implanted medical device, can be taken morefrequently than seizures naturally occur which are recognizable by apatient and/or a patient's caregiver or physician, and therefore theembodiments can provide more sensitive and specific information relatedto effectiveness of a medication than may be obtained from recognizableseizures.

On the other hand, if a drug regimen is not effective, either no changeor an undesirable change in the rate of occurrence of the abnormalpatterns or waveforms of interest would be expected (e.g., as comparedto a baseline or target rate).

In some embodiments, additional changes to a drug regimen (e.g.,additional medication changes corresponding to block 650 of FIG. 6) areinformed by further analysis of the physiological data (e.g.,neurochemical measurements) initially acquired in the assessing stepcorresponding to block 630 of FIG. 6. In the case where the rate atwhich some predetermined “event” is recognized as a “detected event” inthe course of one of these assessments, if there is no change in therate of occurrences of the detected event over time (for example over aday or a week), then a physician may assume that the concentrations ofthe medication are remaining stable at one or more locations of interestin the neural tissue that correspond in some way to the location(s) fromwhich the physiological data is sensed. Thus, the physician may concludethat the drug regimen (e.g., a particular type of medication) is noteffective at controlling the symptoms of the disease. The physician canthen choose, for instance, to increase the dosage of a medication,discontinue a medication, or add a medication in an effort to reach atarget (or cause a change from a baseline).

However, if there are changes in a rate of occurrence of a detectedevent over hours of a day or days of a week, then the physician maydetermine that the concentration of a medication at a location(s) ofinterest in the patient's neural tissue is varying. Variable levelscould be caused, for example, by patient's failure to “comply” withinstructions about how much and when to take a particular drug; thepatient's taking other medications that interact with the medication(s)in the drug regimen; the patient's changing a pattern of behavior suchas regarding exercise or sleep; and changes in hormones such as mightoccur during a patient's menstrual cycle. When the physician determinesthat an issue affecting the effectiveness of a drug regimen is thepatient's compliance with a prescribed drug regimen or the patient'sother behavior, the physician can counsel the patient to comply, or canselect a medication with less stringent dosage requirements, in aneffort to, for example, come closer to a target as is tested in step 640of the flow chart of FIG. 6.

In some embodiments, distinctions can be made between changes in ameasured value (such as a rate of occurrence of a detected event) thatare indicative of the effectiveness of medication and changes in themeasured value that are not indicative of effectiveness and instead areindicative of physiological variation that is random, substantiallyrandom, or otherwise not reflective of the effectiveness of medication.If changes in a measured value correspond in time to changes inmedication dosage, or correlate to medication dosage or changes inmedication dosage, then the physician may determine that the changesobserved are genuinely due to changes in the effectiveness of amedication. In these circumstances, if the changes in the particularmeasured value are not associated in time with a medication change, thenthe physician may determine that the changes observed are not related toeffectiveness.

In some embodiments, a system including an implantable medical device100 can determine and indicate to the physician whether changes in ameasured value are related to effectiveness using information related tomedications and dosage, including time and/or date of any changes inmedications or dosage entered into a user interface by the physician orpatient. In other embodiments, a system including an implantable medicaldevice 100 can estimate short-term variation in a measured value, suchas by calculating the standard deviation of a set of measured valuescollected over a 24-hour period at one-hour intervals, and can indicateto the physician the proportional relationship between changes in themeasured value that occur at longer intervals (such as 28-day intervals)when medication dosage was changed, and the short-term variation. Instill further embodiments, a system or method can indicate to thephysician that changes in a measured value that occur at intervalsassociated with dosage changes and are, e.g., greater than two standarddeviations calculated as described above are indicative of effectivenessof medication, whereas changes in a measured value that are smaller thantwo standard deviations may not be relevant to effectiveness ofmedication.

Further, if the effectiveness of a given drug regimen seems to vary overmonths based on the information provided or otherwise generated by theimplantable medical device 100, then the physician may determine thatthere are longer term changes in concentration of one or more of themedications such as might occur with changes in renal or liver functionor with changes in weight, or that a medication is losing itseffectiveness over time. In these situations, the physician may choosefor instance to increase the dose of a medication in an effort torestore its effectiveness or to switch the patient to a medication thatis expected to be less sensitive to liver or renal function.

In some embodiments, such as when a patient is being subjected to a drugregimen to treat epilepsy, changes in physiological data that correlatewell to whether a drug regimen is effective may include changes that maybe measured by any of the following metrics: decreases in the number ofdetected abnormal electrographic events; decreases in rate ofoccurrences of conditions of the implantable medical device 100 causedby abnormal electrical activity of interest, such as a decrease in thehow often amplifiers in the device are saturated; decreases in theduration of a given “detected event”; decreases in the number of shiftsin pH of extracellular fluid; decreases in the number of tissue spikesin oxygenation of tissue (such as tissue comprising the brainparenchyma); decreases in the excitatory neurotransmitters such asglutamate; or increases in inhibitory neurotransmitters such as gammaamino butyric acid (GABA).

In embodiments in which an implantable medical device is configured tomonitor decreases or increases in neurotransmitters, these decreases orincreases can be measured using voltammetry. Voltammetry is a family ofanalytic methods in which the voltage of a working electrode ismanipulated with respect to a reference electrode, and the resultingcurrent flow is measured. The characteristics of this current flow, suchas small changes in the shape or amplitude of current when plottedagainst voltage, are indicative of the electroactive species present (inother words, the chemical species present that participate inelectrochemical reactions) and their concentrations. Decreases orincreases in neurotransmitters, such as glutamate or GABA, can also bemeasured using fixed potential amperometry at enzyme-linked biosensors,in which current flow through a sensor is modified by biochemicalreactions that occur in the presence of neurotransmitters, and wherethis current flow is indicative of the amount of the neurotransmitterpresent in the surrounding solution. In embodiments in which animplantable medical device 100 is configured to measure shifts in pH ofextracellular fluids caused by changes in neural activity, such shiftscan be measured by pH electrodes such as ion-sensitive field effecttransistors (ISFETs) sensitive to hydrogen ions, or by usingvoltammetric techniques as described above, for instance, withpH-sensitive wire electrodes such as metal oxide electrodes.

If embodiments reveal to a physician that a change to a drug regimenshould be tested, then the physician can instruct the patient tocontinue to perform adjustments of the medication dosage to achievefurther improvement or to maintain the current medication regimenwithout bringing the patient into the office. If no improvement in thephysiological data (e.g., desirable changes in the levels of aneurochemical) occur at a dose that would be expected to be effective orat a dose that is eliciting side effects, the physician can instruct thepatient to discontinue the medication. This may be desirable tominimizing side effects a patient experiences due to a given drug, orminimize the costs associated with a given drug (e.g., reduced dosage,lower cost). It will be apparent that having a quantitative assessmentof the effectiveness of a drug regimen may be of great benefit to aphysician in making the decisions about the drug regimen (such aswhether to continue or discontinue a particular medication includedwithin the drug regimen).

In sum, embodiments of the method described in the flow chart of FIG. 6may provide one or more of the following advantageous results: First,the effectiveness of a patient's drug regimen may be monitored by aphysician at least in part, based on information the physician has aboutthe drug regimen the physician put the patient on as well as informationwhich the implantable medical device is configured to produce and, forexample, transmit to the physician when the patient uses an externalcomponent, such as a patient remote monitor 362 to transmit informationfrom the implantable medical device 100 to the physician's programmer362 or to a database in the data management system 360 which thephysician can access, for example, via a website interface. This mayresult in fewer face-to-face visits between the patient and physicianfor the purpose of titrating or calibrating the patient's drug regimen.Second, a physician can use the data produced or generated by theimplantable medical device 100 during the assessment as an indicator ofwhether the patient is likely complying with the drug regimen thephysician has prescribed. Third, the physiological data operated on bythe implantable medical device 100 (and one or more metrics associatedtherewith or derived therefrom) may provide an objective measure ofeffectiveness of a given drug regimen. This may be important when thepatient is being treated for epilepsy, for example, since theeffectiveness of a drug regimen otherwise is determined, at least inpart, by the number of seizures the patient recognizes that he or she ishaving. More particularly, epilepsy patients are typically asked tomaintain some sort of a log (commonly referred to as a “seizure diary”)in which the patient records the dates and times the patient thinks theyare experiencing a seizure. (Since a given electrographic seizure maynot be perceived by a patient as a seizure, in the best case, thepatient's seizure diary will only represent a record of the patient's“clinical seizures” (or the seizures for which there areclinically-observable symptoms). In other than the best case, thepatient may underreport his or her clinical seizures in his or herseizure diary, for example, because the patient may not remember aseizure or may remember a seizure but forget to make an entry in his orher seizure diary. Thus, for several reasons, a patient's reportedseizures in a seizure diary often is a subjective record of seizures andoften not a very reliable one at that. Fourth, the physiological changes(including but not limited to neurochemical changes) produced by themedications and observed and tracked by the implantable medical device100 often may precede reported changes in clinical symptoms. Fifth, aphysician may assess whether a lower dose (including no dose) of aparticular drug may be equally effective for the patient given therelevant baseline or target, and the lower dose may be better toleratedby the particular patient (e.g., in terms of toxicity or unpleasant sideeffects). Finally, determining whether a medication is ineffective canbe accomplished quickly and objectively.

FIG. 7 is a schematic illustration of a system according to embodimentsgenerally in the form of a block diagram, for assessing theeffectiveness of and/or adjusting a parameter of a drug regimen or otherdrug therapy to which a patient is subjected for treatment of aneurological disorder.

A center block 700 in FIG. 7 represents a collection of componentsdescribed previously including an implantable medical device 100,sensors/probes associated with the implantable medical device (e.g.,electrode-bearing brain leads 114, 116, a probe configured to acquirevoltammetry measurements, a probe configured to obtain an oxygenconcentration measurement, etc.), external components with which theimplantable medical device 100 may communicate, such as one or moreprogrammers 362, a patient remote monitor 362, and a data managementsystem 360 or a website interface and/or a database or set of databasesthereof.

The inputs to the components represented by the center block 700 mayinclude one or more of information corresponding to “detected events” inneural activity (e.g., electrographic activity) that is defined asconstituting pathological activity (or other identified characteristicsof physiological data) 702, duration of detected events (or otheridentified characteristics of physiological data) 704; rate ofoccurrences of detected events (or other identified characteristics ofphysiological data) over time 706, pH 708; tissue oxygenation 710;neurotransmitter levels 712; or amplitude of evoked potentials 714(which evoked potentials are described in more detail below).

In addition to the system inputs (or potential system inputs) 702, 704,706, 708, 710, 712, and 714, other data may be used in embodiments inassessing the effectiveness of a drug regimen, including datacorresponding to the medications a patient may be currently taking(“current medications” 720), and data corresponding to a historicalperspective of the medications or drug regimens to which the patient hasbeen subjected (e.g., over a long term or a relatively short term)(“medication history”) 722.

Where a patient is implanted with a medical device that is configurableto deliver or which has been delivering a form of stimulation to thepatient (for example, a form of electrical stimulation therapy), stillother data may be used in embodiments in assessing the effectiveness ofa drug regimen, including data relating to the set of stimulationparameters according to which stimulation waveforms are generated andoutput from the implantable neurostimulator and to which location(s) inthe patient's neural system the stimulation is delivered (e.g., to whichelectrodes on which brain leads 114, 116) (“current stimulationparameters” 724). It will be appreciated that if the form of stimulationis being delivered to a patient using other than an implantedneurostimulator (e.g., by introducing optical stimulation to the brainthrough a probe that is only partially implanted in the brain), thenvalues for current stimulation parameters 724 may also exist.

Where a patient has an implanted neurostimulator (or otherwise has beenreceiving a form of neurostimulation, as from an optical stimulationsource), there may exist a history of that previously deliveredstimulation as may be defined, for example, by a set of stimulationparameters. Such “stimulation parameter history” information 726 alsomay be used in embodiments to assess whether a drug regimen iseffective.

One or more outputs corresponding to the components represented in thecenter block 700 may be useful in adjusting either the parameters of adrug regimen or, if applicable, the parameters of another form oftherapy the patient may receive, such as a form of electricalstimulation therapy, in response to a given assessment of theeffectiveness of a drug regimen. For example, the effectiveness of agiven drug therapy may be improved by either or both of adjusting aparameter of the drug therapy and adjusting a parameter of an electricalstimulation therapy. More specifically, it may be the case that theeffectiveness of a drug therapy may be improved, not by increasing thedose of a drug, but rather by adding a form of electrical stimulation(or adjusting a parameter of an electrical stimulation therapy currentlybeing delivered) so that the electrical stimulation is directed to oneor more locations of interest in the neural tissue (e.g., at thelocation of a stimulating element 344). Conversely, the effectiveness ofa given electrical stimulation therapy may be improved not by increasingthe amplitude or pulse width with which the stimulation ischaracterized, but rather by adding a medication or otherwise adjustinga parameter of a drug regimen.

In some embodiments, an overall effectiveness value for a given therapyor combination of therapies intended to modulate behavior of a patient'sneural system using a combination of the system inputs 702, 704, 706,708, 710, 712, 716, the patient's drug regimen 720 and drug regimenhistory 722, device-specific data such as the current stimulationparameter 724 and the historical stimulation parameters 726. Such anoverall effectiveness value may be displayed numerically or presentedgraphically. For example, in the plot 732 shown at the bottom of FIG. 7,the rate at which an overall effectiveness value changes over time (inunits of days) is graphed for a user.

In one embodiment, an overall effectiveness value for a givenneuromodulation therapy (e.g., comprising a drug therapy and anelectrical stimulation therapy) may be calculated using a combination ofthe data and by multiplying the number of electrographic seizuresdetected per week by the implantable medical device 100 by the averageduration of the electrographic seizures. This calculation yields a valuethat is descriptive of the total time per week spent in anelectrographic seizure, and it will be apparent that relatively lowvalues such as one minute per week may be associated with effectivenessof a given neuromodulation therapy whereas relatively high values suchas 1000 minutes per week may be associated with lack of effectiveness ofthe therapy.

The value yielded by this calculation may be compared to a not-to-exceedtarget such as not to exceed five total minutes per week ofelectrographic seizure (which are defined for the implantable medicaldevice to comprise “detected events”). This information can then be usedby a physician with knowledge of the patient's current drug regimen 720,medication history 722, and, optionally, stimulation parameters 724 andstimulation parameter history 726 (if the neurostimulator is configuredto deliver stimulation) to adjust medication types and levels, forexample, in accordance with the flowchart of FIG. 6.

It will be apparent that several elements in the flow chart of FIG. 6can be a physician or the implantable medical device 100 or acombination thereof. For instance, a physician can determine anappropriate medication change guided by an overall effectiveness valuecalculated and displayed by one or more of the components in the centerblock 700 of FIG. 7 (e.g., an implantable medical device 100 and anexternal programmer component 362). In an alternate embodiment, thesystem may enable the implantable medical device 100 (if the implantablemedical device is provided with information related to the patient'scurrent medications 720 and medication history 722) to automaticallysuggest an appropriate adjustment of medications 730 guided by this sameeffectiveness value. In a further embodiment, an implantable medicaldevice configured to deliver neurostimulation 100, if the implantablemedical device is provided with information related to currentstimulation parameters 724 and stimulation parameter history 726, canautomatically suggest an adjustment of stimulation parameters 728 thatis guided by the system inputs 702, 704, 706, 708, 710, 712, and 714 aswell as by the physiological data itself (e.g., stored electrographicsignals or representations thereof) and that is appropriate given thecurrent medications 720.

FIG. 8 is a histogram showing, on the y-axis (or vertical axis) a numberof “detections per day” and, on the x-axis (or horizontal axis) thepassage of time in days. The metric that results in the “detections perday” may be one of a great many possible metrics, such as a number ofelectrographic seizures detected per day, a number of electrographicseizure precursors detected per day, a number of spikes detected perday, the number of times the concentration of a neurotransmitter roseabove a certain threshold, the number of times the oxygen or pH levelfell below a certain threshold, and so on and so forth. In short, the“detections per day” can correspond to the rate at which somethingoccurs that the implantable medical device 100 is configured to detector otherwise identify. For ease of description, the “detections per day”represented in FIG. 8 may result from the implantable medical device 100being programmed (according to its set of detection parameters) tocontinuously log in the event counting/logging module 322 when aparticular type of epileptiform “event” is “detected”, to calculate arate of detection of the logged events over each successive 24-hourperiod, and then to log the average number of events detected per day.The average number of events detected per day by the implantable medicaldevice 100 thus may result in the “detections per day” for a patientshown in FIG. 8. These data may be uploaded from the implantable medicaldevice 100 to a host device, such as one of the external components(e.g., the programmer or patient remote monitor 362 or the datamanagement system 360). The physician may monitor the “detections perday” at a location remote from the patient by viewing the data uploadedfrom the patient's implanted device and accessible from one or more ofthe external components.

FIG. 8 is meant to show that the number of “detections per day” variesas the dose of a particular drug being administered to the patientvaries. For example, for the first 10 days, the graph shows the numberof “detections per day” by the implantable medical device varies betweenabout 1800 detections per day (e.g. the “detections per day” at Day 6810) and 2500 detections per day (e.g., the “detections per day” at Days4 812 and at Day 10 814).

At the 10-day mark, the physician instructs the patient to start takinga new medication at a daily dose of 500 mg. The drug might be anantiepileptic medication such as levetiracetam. After the patient beginstaking the 500 mg dose of the new medication and over the next ten days,the “detections per day” decrease to vary from between about 1600detections per day (e.g., “detections per day” at Day 15 816) to about2000 detections per day (e.g., “detections per day” at Day 17 818). Fromthis data the physician may infer that the 500 mg dose is effective inreducing the “detections per day.”

Assuming that reducing the “detections per day” is one of thephysician's objectives and the patient is experiencing no adverseeffects from the drug, the physician may choose to try increasing thedose, to see if in so doing the “detections per day” are furtherreduced. In this circumstance, the histogram of FIG. 8 shows that, whenthe patient's dose of the same drug is increased from 500 mg to 1000 mgper day, the “detections per day” further decrease to vary between fromabout 1200 detections per day (e.g., “detections per day” at Day 28) toabout 1500 detections per day (e.g., “detections per day” at Day 21820).

FIG. 8 further shows that the number of “detections per day” continuesto be reduced as the dosage of the drug is increased, such that at adaily dose of 2000 mg, the “detections per day” vary between from aboutless than 100 detections per day (e.g., “detections per day” at Day 42824) to about 500 detections per day (e.g., “detections per day” at Day41 826). Thus, the physician can see that the “detections per day”continues to decrease as the physician titrates the dose from an initialdose of 500 mg through intermediate doses of 1000 and 1500 mg up to 2000mg. Monitoring the “detections per day” using the implantable medicaldevice allows the physician to assess which dose of the drug is mosteffective up to some predetermined maximum (e.g., the maximum dose forthe drug for this particular patient may be 2000 mg per day). The dataobtained from the implantable medical device 100 may be of substantialvalue clinically because seizures (clinical or electrographic) will notalways occur when the patient is present with the physician in thephysician's office and because relying only on the patient's seizurediary alone as a measure of seizures is not especially reliable (due topatients underreporting or misreporting seizures). A physician mayassess whether a particular dose of a drug is effective in treating adisorder of a patient more quickly and less ambiguously than if thephysician were to rely only on patient-reported seizures or seizuresotherwise observed or recorded in a clinical setting to assesseffectiveness.

In another circumstance, and referring now to FIG. 9, a histogramsimilar to that shown in FIG. 8 is used to illustrate that embodimentscan be used to assess when further changes in a patient's drug regimenhave no incremental beneficial effect such that, for example, the doseof a drug should not be increased beyond a certain level. In FIG. 9, onthe y-axis (or vertical axis) the medium duration of a long episode (inseconds) is plotted versus time in days on the x-axis (or horizontalaxis) the passage of time in days. A “long episode” may be defined forthe implantable medical device 100 by its programmable detectionparameters as a type of pathological electrographic activity thatpersists (e.g., continues to be detected when sampled) over at leastsome minimum period of time, such as at least one second. For example,the implantable medical device 100 may be configured to recognize andtherefore “detect” a long episode whenever an amplifier in the sensingmodule 312 is saturated at least once as a result of the input signal.The data logged by the implantable medical device 100 may be uploadedfrom the device to one or more host devices, such as the externalcomponents comprising the programmer or the patient remote monitor 362and/or the data management system 360. During a patient's visit to thephysician's clinic, the physician may retrieve data relevant to the“long episodes” detected by the implantable medical device 100 from astorage location such as in a database of the data management system 360for review.

For the first 10 days, the patient is either on a drug regimen that isnot effective in reducing the duration of long episodes or is notreceiving any drug therapy at all. During this first 10 days, the datafrom the implantable medical device suggests that the patient isexperiencing long episodes of at least 125 seconds each day (e.g., thelong episodes of at least 125 seconds at Days 1-10 910). At the 10-daymark, the physician may introduce a new antiepileptic drug to thepatient, such as valproate, starting the patient at a dose of 500 mg.

Upon introducing the new drug to the patient at the 500 mg dose, thelong episodes appear to decrease from an average of at least 125 secondsto an average of 90 seconds (e.g., for Days 11-20 920). A shorterduration of a long episode may be correlated to less pathologicalactivity occurring in the patient's brain and therefore reducing thelength of the long episodes may be an objective of therapy for thepatient.

The drug appears to be having a desirable effect on the duration of thelong episodes up to a dose of 1500 mg (i.e., at an intermediate dose of1000 mg, the median duration of a long episode shortens to about 70seconds (for Days 21-30 930) from the 90 seconds observed during Days11-20 920. After the dose is increased to 1500 mg, the median durationof a long episode drops to about 30 seconds and stays at that durationfor about 12 days (for Days 30-42 940). However, when the dose isincreased to 2000 mg over the next eight days, the median duration of along episode remains steady at 30 seconds (for Days 42-51 950). So thephysician drops the dose back down to 1500 mg (at Days 51-60 960) wherethe median duration of the long episodes the patient experiences remainsstable at about 30 seconds. Thus, embodiments for assessing theeffectiveness of a drug can be used to avoid having the patienthabitually receive a dose of the drug that is higher than the dose whichis effective for providing the desired therapy.

Referring now to FIGS. 10 and 11, embodiments are described wherein theeffectiveness of a drug regimen is assessed relative to one or moreevoked potentials. In these embodiments, an implantable medical device100 is configured to acquire, process, and analyze electrographicsignals sensed from a patient, and to identify one or more features inthe electrographic signals (e.g., an amplitude for each sample of thesignal or an average amplitude calculated from a set of theelectrographic signals as is described more fully below). Theimplantable medical device 100 further is configured as aneurostimulator so that it can generate and output one or morestimulation waveforms which can be delivered to the patient through astimulation/sensing element 340 or a stimulation element 344. Moreparticularly, the implantable medical device 100 may be programmed todeliver one or more stimulation waveforms to a location or locations ofinterest in the patient, and then to recognize one or more features inthe electrographic signals that result when each stimulation waveform isapplied. The one or more features can be stored by the device (e.g., inthe recording module 320), and the implantable medical device 100 mayprocess and analyze the electrographic signals produced as a result ofeach stimulation waveform with the sensing module 312 and/or thedetection module 318. The processing and analysis may accomplish, forexample, some form of averaging of the acquired signals, and the resultsof the processing and analysis may be store in the implantable medicaldevice 100 such as in the event counting/logging module 322.

By way of example and not limitation, the implantable medical device 100may be configured to generate and output a stimulation waveformcharacterized by a set of programmable stimulation parameters. As shownin FIG. 10, one such waveform 1000 may comprise just a single pulse 1010characterized by an amplitude 1012 of, for example 3 mA, a phase width1014 of 120 μS, and an inter-phase interval 1016 of 100 μS. Theimplantable medical device 100 may be programmed to generate and outputthis single-pulse waveform 1000, for example, by instructionsimplemented by the control module 326, according to a predeterminedschedule or otherwise at times triggered by some other criteria (such aswhen the implantable medical device 100 deems that a “detected event”has occurred). The stimulation waveform 1000 then may be delivered tothe patient through one or more designated stimulation elements 344 at alocation or locations from which the patient's response to thestimulation waveform 1000 can be sensed by one or more sensing elements340 (an element through which the stimulation waveform 1000 is deliveredcan also be configurable for sensing, for an example, an electrodelocated on the distal portion of a brain lead 114, 116).

The locations for delivering the stimulation waveform 1000 and sensingthe electrographic activity the patient's neurons produce in response tothe stimulation waveform may be selected based on spatial or temporalconsiderations, or on where in a given functional neural circuit thestimulation waveform is being applied. For example, the stimulationwaveform 1000 may be delivered to one location of interest thatcomprises a region of neural tissue that is different from thelocation(s) at which the patient's electrographic response to thestimulation waveform 1000 is being sensed (for example, a region ofneural tissue that is distant from the sensing location(s) or which isunderstood to have neural projections to or otherwise be incommunication with the sensing location(s)).

In an embodiment, the implantable medical device 100 may be configured,for example, to acquire an electrographic signal in a 300 ms windowfollowing the delivery of a stimulation waveform 1000. This acquiredelectrographic signal may be deemed an “evoked response” since it isexpected to reflect a response of the patient that has been evoked fromdelivering the stimulation waveform 1000 to the patient.

The implantable medical device 100 further may be configured to processand analyze the acquired electrographic signal(s) constituting eachevoked response to identify one or more features in the signal(s), forexample, according to a set of detection parameters that governoperation of the detection module 318. For instance, the implantablemedical device 100 may be configured to measure an amplitude of each ofseveral samples on an evoked response, such as beginning 100 ms aftereach stimulation waveform 1000 has been delivered. The implantablemedical device 100 further may be configured, for example, using one ormore analytical tools implemented in the detection module 318, tocalculate an average amplitude of a set of responses evoked using aparticular stimulation waveform 1000, for example, to reduce the effectof noise and/or random variation in the actual response.

FIG. 10 illustrates graphically several examples of what might be someevoked responses based on the amplitudes measured in the samples overtime for particular evoked responses. For example, four evoked responses1020, 1022, 1024, 1026 are shown in FIG. 10 relative to a y-axis (orvertical axis) of voltage and an x-axis (or horizontal axis)representing the passage of time. The thick line 1028 on the graph ofFIG. 10 represents an average of the four evoked responses 1020, 1022,1024, 1026. It will be appreciated that analytical tools to createaveraged signals may be implemented in the implantable medical device100, in one or more of the external components, for example theprogrammer 362 or the data management system 360, or some combination ofthese.

Evoked responses may be especially relevant to assessing theeffectiveness of drug regimens in the case where a drug regimen is beingused to treat epilepsy. More particularly, epilepsy is a disease inwhich neural tissue often is abnormally excitable (i.e.,over-excitable). So if the amplitude of an evoked response or average ofa given set of evoked responses decreases after a drug is introduced tothe patient (or a change to a parameter of a drug regimen is made, suchas increasing the dose of an existing drug), then this may suggest tothe physician that the tissue from which the evoked response is sensedis less active than it was before the drug was introduced (or otherchange to a drug regimen was made). Thus, a physician may considerdesirable an outcome in which a drug regimen is determined to result ina lower activity level of certain neural tissue may be a desirableoutcome.

FIG. 11 is a histogram 1100 where the y-axis corresponds to the averageamplitude (in microvolts) of evoked responses (also referred to as“evoked potentials” when the amplitude of the evoked responses ismeasured in volts) is plotted over time in days on the y-axis, as thedosage of a drug included in a drug regimen to which a patient issubjected is varied from 0 to 2000 mg. The drug may be one intended totreat epilepsy, such as carbamazepine. FIG. 11 may correspond to adisplay on an external component such as a programmer 362 or a websiteenabled to access a database of the data management system 360 and thedata displayed may be derived from the implantable medical device 100and/or one or more of the external components 362, 360. In thisparticular case, the drug the physician selected appears to have noeffect at any of the doses on the level of activity of the neural tissueas measured by the averaged evoked responses. In other words, theaverage evoked potential amplitude remains stable at about 600 μVregardless of whether the dose of the AED (e.g., carbamazepine) is 0 mg(for Days 1-11 (1102)), 500 mg (at Days 12-21 (1104)), 1000 mg (at Days22-31 (1106)), 1500 mg (at Days 32-41 (1108)) or 2000 mg (at Day 51 etseq. (1110)). Therefore, the physician is likely to conclude from thisassessment that the particular drug is not effective in achieving theobjective of affecting the behavior, at least in terms of activitylevel, of the neural tissue associated with the locations where thesensing element(s) 342 have been situated. Consequently, the physicianmay discontinue the drug (e.g., at about Day 51 (1112) as reflected onFIG. 11).

Referring now to FIGS. 12A and 12B, embodiments are described whereinthe effectiveness of a drug regimen is assessed relative to theconcentration in one or more power bands of electrographic signalsacquired, processed and analyzed by an implantable medical device 100and displayed to a user, for example, on a display associated with oneor more of the external components, such as a programmer 365 or awebsite through which a user may interface with a data management system360.

In these embodiments, an implantable medical device 100 is configured toacquire, process, and analyze electrographic signals sensed from apatient, to identify one or more features in the electrographic signals,such as features that correspond to the power of the signal inparticular frequency bands, such as the band from about 13 Hz to about30 Hz. For example, a detection module 318 of the implantable medicaldevice 100 may be configured with a set of programmable detectionparameters to identify when the electrographic signals exhibitfrequencies in the 13-30 Hz band using an analytical tool that uses afast Fourier transform (FFT), filter banks, wavelet transforms, orhalf-wave spectra. The implantable medical device 100 or one of theexternal components 362, 360 or the implantable medical device and anexternal component together may be configured to calculate and generatea display evidencing changes in power of the acquired electrographicsignals over time. Techniques such as smoothing by averaging, forexample with a cosine window having a duration of one day may be used,for example, to improve the ease with which a user can appreciate theresults. (A cosine window is one means for smoothing a rapidly-varyingsignal, where each measurement is replaced by a weighted average of thenearby measurements. The amount of weighting is determined by afunction, such as a cosine function, whose highest value is at 0 (i.e.,the central measurement in question is weighted most highly) and whosevalue decreases in either direction, weighting other values less andless as they become more distant from the central value.)

Each of FIG. 12A and FIG. 12B is an example of a display that might beprovided to a user related to an assessment of the effectiveness of adrug using power band information according to embodiments. The line1202 in the graph 1200 of FIG. 12A represents the variation over time ofthe power of the electrographic signals acquired by the implantablemedical device 100 in a 13-30 Hz power band (y-axis) over a given periodof time (x-axis). The spectrogram 1250 of FIG. 12B is an alternative wayof displaying the results displayed in FIG. 12A, and illustrates thetotal power in the 13-30 Hz frequency band of interest where the y-axiscorresponds to frequency (in Hz) and the y-axis corresponds to time (indays).

In disorders such as Parkinson's disease, abnormal physiology may becharacterized by the occurrence of high-power beta band oscillations inone or more electrographic signals being monitored from the patient'sbrain. The “beta band” corresponds to frequencies in the range of 13-30Hz. In other words, the patient may experience one or more unpleasantsymptoms of the movement disorder when the electrographic signalsexhibit a lot of power in the 13-30 Hz frequency range and it thereforemay be desirable to reduce power that occurs in that frequency range inthe monitored signals in order to achieve a positive therapeutic resultfor the patient. According to embodiments, the effectiveness of a drugregimen in reducing the power of the monitored electrographic signals inthe beta band may be calculated as the inverse of the power value shownin FIG. 12A.

In a particular example, and with reference to FIGS. 12A and 12B, aphysician may start a patient on an anti-Parkinson's medication, such asa drug classified as a dopamine precursor. A marker 1254 at about Day 48is shown on each of FIGS. 12A and 12B to indicate the day on which thepatient starts the new medication and then, after an elapsed time 1256of about 20 days, the patient begins taking a higher dose of the newmedication. The two graphs suggest that the effect of the new medicationis to decrease the power of the monitored signal occurring in thefrequency band of interest (i.e., the beta band), and that the power inthe beta band decreases even further after the patient increase the doseof the new medication. More particularly, and with reference to FIG.12A, the power in the beta band decreases in the elapsed time 1256 ofabout 20 days after the patient is started on the new medication, andthen decreases further in the elapsed time 1260 at about the Day 68marker 1258 et seq. Therefore, the physician is likely to conclude fromthis assessment that the particular drug is somewhat effective inachieving the objective of affecting the behavior, at least in termsdecreasing the amount of the signal occurring in the beta band monitoredfrom the neural tissue using the locations where the sensing element(s)342 have been situated.

FIG. 13 illustrates an example of an interactive display and some of thesources from which the data displayed might be drawn according to someembodiments for assessing the effectiveness of a drug regimen. Thedisplay 1300 may be viewable by a user on a website in communicationwith a remote data management system 1302 (such as data managementsystem 360) and/or with a local data store 1304 (such as might beresident on or otherwise associated with a programmer or remote monitor362).

The particular example shown in FIG. 13 assumes that, in addition tobeing subjected to a drug regimen, the patient is receiving (or mayreceive) a form of electrical stimulation (as may be delivered by animplantable medical device 100 configured as a neurostimulator fordelivering an electrical stimulation therapy, or perhaps, a stimulationwaveform to be used in evoked response analysis).

The display 1300 shows a user a patient's medication history 722 (here,a history of changes to the dose of carbamazepine (from 500 mg to 1500mg) the patient has been receiving over the past 63 days) and astimulation parameter history 726 (here, electrical stimulationwaveforms 530, 540 characterized by an amplitude 518 of 5 mA and a burstduration 536 of 100 ms for the past 70 days). A graph 1306 provides theuser with data showing the variation over a period of days of some valuebelieved to correspond to the effectiveness of the drug regimen overtime, including the period covered by the historical medication changes722 and the stimulation parameter history 726. As discussed elsewhereherein, the value may relate to any measure or metric deemed relevant todrug regimen effectiveness, including “detections per day” (FIG. 8),long episode duration (FIG. 9), average amplitude of evoked responses(FIG. 11) and changes in power of a monitored signal in a particularfrequency band (e.g., the beta band) (FIGS. 12A and 12B).

The display 1300 may be an element of an interactive interface (e.g., agraphical user interface or “GUI”) of a website associated with theremote data management system 1302 or of an interactive interface with alocal data store 1304 with another external component, such as aphysician programmer 362. An interactive interface may include an inputprompt 1308 prompting the physician to input changes to a drug regimen,such as an increase or decrease in the dose of a drug the physicianwants the patient to take. An interactive interface may also include afeature that invites a user to ask for an “optimal dose” analysis, suchas by a touch screen button such as the touch screen button 1310 labeled“analyze optimal dose” in FIG. 13. An optimal dose analysis may involvecalculations and the execution of algorithms designed to project, for agiven drug or combination of drugs, a level of effectiveness based onfactors such as: the patient's history with other drug regimens and/orwith other forms of therapy intended to modulate neural behavior (e.g.,electrical stimulation therapy); the patient's (or a patientcaregiver's) reports of the manifestations or symptoms of a disorder(such as reports of seizures in a patient-maintained “seizure diary” ora log of tremors, or disruptions in sleep); other patient-specificfactors (such as sex, weight, age, etc.); and, perhaps, factors relatedto a demographic into which the patient falls (such as patients whoexperience epilepsy where the seizures are believed to originate from aparticular “focus” such as the mesial temporal lobe or a hippocampus).

As mentioned elsewhere herein, it is believed that different forms oftherapy delivered in an effort to treat a given patient's particulardisorder can interact in synergistic or antagonistic ways. Thus, itwould be desirable to exploit the synergies and minimize theantagonisms. An example of a synergy is when the effect of stimulationalone is less than the effect of a combined stimulation and drugtherapy. A similar example of a synergy is when the effect of a drugtherapy alone is less than the effect of a combined stimulation and drugtherapy treatment.

More complex examples of synergies would be when the overall effect of acombination of therapies (such as a combination of a drug therapy and anelectrical stimulation therapy) can be adjusted by changing one or moreof the parameters of each of the forms of therapy, so that thecombination therapy can effectively be “fine tuned” for a given patientto achieve what the physician deems to be an optimal result. Forexample, patients with epilepsy who are taking medications that blocksodium channels may achieve better seizure control if they are providedwith stimulation that produces a depolarization block (e.g., depolarizescells and blocks neuronal firing and therefore neural activity).Stimulation programmed to high frequency (100 Hz or more) and moderateburst durations (100 ms to 1 s) can result in these “depolarizationblocks”.

In the implantable medical device 100, stimulation parameters such asburst duration 536 or the inter-pulse interval 524 could be adjusted toresult in depolarization block. For instance, the inter-pulse intervalcould be decreased by 1 ms increments resulting in increases in thefrequency of stimulation which would increase the likelihood thatstimulation would produce a depolarization block. In addition the burstduration could be increased by 100 ms intervals which would alsoincrease the likelihood that stimulation would produce a depolarizationblock of neuronal firing. In another example, patients takingmedications that treat seizures by increasing the neuronal response toinhibitory neurotransmitters such as GABA may achieve the best seizurecontrol when treated with stimulation that drives the activity ofneurons to increase the release of neurotransmitters such as GABA.Stimulation programmed to low frequency (1-50 Hz) and long burstdurations (1 sec) may drive activity in neurons and increase the releaseof neurotransmitters.

In the implantable medical device 100 stimulation parameters such asburst duration 536 or the inter-pulse interval 524 could be adjusted todrive neuronal activity and release of neurotransmitters. Morespecifically the inter-pulse interval could be increased by 1 msincrements to reduce the stimulation frequency and or the burst durationcould be increased by 100 ms increments starting at 1 sec. Thusadjusting a stimulation parameter (e.g. increasing or decreasing theinter-pulse interval) may be beneficial to a patient with epilepsy.Furthermore the direction of the stimulation parameter adjustments orranges, for example the inter-pulse interval adjustment (increase ordecrease), that may be beneficial to the patient can be dependent on thetype of medication the patient is taking.

Conversely, for a patient that is receiving combined drug andstimulation therapy the type of medication that a physician chooses toadd to a patient's drug regimen may be dependent on the stimulationparameters being used to treat the patient's disorder.

In each of these cases where a combination of therapies is delivered, itwould be beneficial to provide the physician with useful feedbackconcerning the effect the adjustment of one parameter of a therapy mayhave on the overall result of the combination of therapies. Embodimentsdescribed herein are intended to provide such useful feedback.

As presaged by the description of FIGS. 5A-5C, an electrical stimulationtherapy delivered to a patient can be configured according to a greatmany parameters and, in many case, each parameter may have a valuewithin a range of possible values. The set of stimulation parametersincludes, for example, pulse parameters such as a leading phase 512, atrailing phase 514, and a phase width 516, a pulse amplitude 518, and anoverall pulse morphology (e.g., whether the two phases are characterizedby the same amplitude and phase width or different amplitudes and phasewidths), an inter-phase interval 520, an inter-pulse interval 524, aburst 532, 534 characterizable by a number of pulses in a burst, a burstduration 536, 538, a burst morphology (e.g., whether a burst begins witha “ramp up” period 564 and/or a “ramp down” period 566), whether a burstor set of bursts or pulses is characterized by a duty cycle such thatthere is a stimulation “on time” 560 and a “stimulation off” time 562,and so on and so forth. Additionally, it will be appreciated that theconfiguration of the stimulation pathways will also play a role in thepatient's response to a given form of electrical stimulation based onwhere the stimulation elements 344 are located, whether the stimulationelements 344 are in a functional neural circuit or otherwise spatiallyadjacent to a source of pathological physiological activity, such asseizure focus, etc.

Preliminarily, some of the likely consequences will be described ofparticular parameter choices for various features of electricalstimulation therapy, such as pulsatile electrical stimulation, and ofparticular parameter choices for various features of a drug regimen.This description is meant to facilitate later discussion herein ofembodiments in which parameters of a combination therapy are adjusted inorder to exploit a synergy (such as electrical stimulation improving theeffect of a drug) or minimize an antagonism (such as a drug interferingwith the effect of stimulation).

A physician may select a drug or set of different drugs with which totreat a patient with a neurological disorder based on a variety ofconsiderations. Generally, medications used to treat diseases of thenervous system have different effects at specific neural locations orcircuits and produce different neuronal responses. For example, somemedications act on ion channels located on the neuronal membrane andthereby directly alter the threshold for neuronal firing. Somemedications block sodium channels and thus inhibit neuronal firing.Physicians often select drugs in this “sodium-channel blocker” class totreat epilepsy, a disease that is characterized by hyperactivity ofneurons.

Some other medications block the response to or release of excitatoryneurochemicals such as glutamate. Other medications inhibit neuronalactivity by increasing the release of or enhancing the response to (suchas benzodiazepines) inhibitory neurotransmitters such as GABA andglycine. Still other medications prevent the degradation or reuptake ofneurotransmitters (e.g., selective serotonin reuptake inhibitors)prolonging their effect at the synapse.

In an example, a physician may be treating a patient with epilepsy witha drug therapy and with a form of electrical stimulation therapy (suchas delivered using an implantable neurostimulator configured from theimplantable medical device 100 described elsewhere herein). Morespecifically, the patient may be taking a medication, such ascarbamazepine, that blocks sodium channels in neurons to reduce theactivity of the neurons. Such a patient's seizure activity may befurther controlled if the electrical stimulation is delivered accordingto parameters that are expected to result in depolarization block ofsodium channels resulting in blocking neuronal firing and thereforediscouraging neural activity. Stimulation parameters that may beimplicated by this desired therapeutic outcome are the amplitude 518 (ofthe current or voltage used for the stimulation pulses 510), phase width516, frequency (or the inverse of the inter-pulse interval 524) andburst duration 536, 538.

In another example, a physician may be treating a patient with epilepsywith a drug therapy and with a form of electrical stimulation therapywhere the patient is taking a medication that increases the neuronalresponse to inhibitory neurotransmitters (such as GABA), resulting inless neural activity. In this case, if there are certain stimulationparameters or stimulation parameter values that are known or suspectedto also encourage neurons to release inhibitory neurotransmitters, thenthe stimulation parameters or parameter values could be selectedaccordingly to complement the action of the drug and thus drive theneurons to increase release of the inhibitory neurotransmitter ofinterest.

In still another example, a physician may be treating a patient withepilepsy with a drug therapy and with a form of electrical stimulationtherapy where the patient is receiving a form of a stimulation that iscorrelated with a reduction in the rate of seizures the patient isexperiencing, for example, on a daily (or monthly) basis. The parametersof the stimulation, however, may be approaching some not-to-exceedcharge limit (e.g., established as a safety precaution) which limit isdriven in part by the physical components of the stimulation system(e.g., the surface area of the electrodes through which the stimulationis being delivered). In this circumstance, the physician may choose toincrease the dose of a drug the patient is taking that also is expectedto tend to reduce the daily (or monthly) seizure rate rather thanchanging any of the parameters according to which the electricalstimulation is delivered.

Based on the foregoing discussion, it should be appreciated that thereare a great many variables at issue whenever an electrical stimulationtherapy or a drug therapy, or a combination of the two therapies, areprovided to a patient. The situation may be as complicated or even morecomplicated if therapies other than drug and electrical stimulation areincluded in a given combination, or if more than one type of drugtherapy is provided to a patient (such as some drugs ingested orally bythe patient, and others delivered automatically (e.g., by an implanteddrug delivery device in response to some local trigger). Moreover, onlysome of the variables are known; it is not necessarily uncommon for abeneficial effect of a therapy to be appreciated and understood beforethe precise mechanism by which the effect is achieved is evident. Forexample, a physician may know that a particular drug leads to abeneficial outcome but the way in which that drug acts at the molecularlevel or otherwise at a location of interest in the nervous system, maynot yet have been discovered.

In light of these great many variables that are implicated in thedifferent possible forms of therapy for a particular disorder of thenervous system, a physician likely always will have to resort to somedegree of “trial and error” in fine tuning the parameters of a giventherapy to achieve a desired outcome for a particular patient. However,embodiments of the system and method described herein are designed tomake the tuning process less burdensome, in part by relying on feedbackfrom an implantable medical device relating to the impact each parameteradjustment has, if any, on the patient. Such feedback may be used toassess the effect of a given parameter change (e.g., adding a new drugor adding a new stimulation waveform or a new stimulation pathway) or ofa given change in the value of a parameter (e.g., increasing the dose ofa drug in an existing drug regimen or decreasing the total chargedelivered to a patient during a burst of electrical stimulation). Thefeedback can be used to inform decisions (by a physician, by animplantable medical device, or by a physician and device acting inconcert) to make further adjustments to one or more therapies a patientis receiving for a particular disorder.

FIG. 14 is a flowchart of a method according to embodiments forselecting one or more medications to increase the effectiveness of anelectrical stimulation therapy generated by, for example, an implantablemedical device 100 described elsewhere herein configured as aneurostimulator. The stimulation may be delivered to the patient throughone or more stimulation pathways configured using the implantablemedical device 100 and one or more of the stimulation element 344 andsensing/stimulation element 340.

In some embodiments, a goal or objective of an electrical stimulationtherapy is determined (as indicated by the flow chart block 1410); anevaluation is undertaken of the pros and cons of particular electricalstimulation parameters or parameter values for the therapy relative tothe goal (as indicated by the flow chart block 1420); a drug regimen isselected in light of the stimulation goal and the evaluation of thestimulation parameters (as indicated by the flow chart block 1430); andthe patient begins the drug regimen (as indicated by the flow chartblock 1440).

Generally, due to physical or design limitations of a givenneurostimulation system, while stimulation can be delivered to one ormore stimulation locations, such as stimulation locations at or in thevicinity of a stimulation element 344 or in a functional neural circuit,all the neurons in the vicinity of the stimulation element 344 (orotherwise in the pathway the current follows) will be affected by thestimulation. Put another way, stimulation parameters that increaseactivity and thereby increase neurotransmitter release can benonselective. For instance, a physician might decide that a patient withepilepsy would benefit from an increase in the release of the inhibitoryneurotransmitter GABA at the seizure focus. Stimulation to increase GABArelease at the seizure focus would also increase the release of anyexcitatory neurotransmitters at the seizure focus which could bedetrimental to the patient. Adding felbamate, an antiepilepticmedication which acts to both, inhibit excitatory neurotransmitterreceptors and enhance the effect of GABA, would reduce or remove theeffect of stimulation on excitatory neurotransmission and enhance theeffect of the stimulation induced increase in the release of inhibitoryneurotransmitters.

In some circumstances, one or more medications may be used in concertwith an electrical stimulation therapy in an effort to enhance theeffect the electrical stimulation on the neurons one wants to effect andto minimize the effect of the electrical stimulation on the neurons onedoes not want to affect. Embodiments for achieving these objectives aredescribed below, with reference to the flow chart of FIG. 14 and“determining goals of stimulation” and “assessing undesirable effects ofstimulation.”

A given goal may be informed by the effect one would expect stimulationaccording to certain parameters to have at the stimulation location. Forexample, goals of stimulation might include one of the following: reduceneural activity by producing a depolarization block; inhibit neuralactivity by increasing activity of inhibitory interneurons at thestimulation location or by activating an inhibitory projection to adifferent brain region; increase activity by increasing activity at alocation of interest or increasing the release of excitatoryneurotransmitters produced by that location or increasing activity at adistant region by activating excitatory projections to said region; toincrease activity at a location of interest by inducing long-termpotentiation (LTP); long lasting enhancement in signal transmission thatoccurs between neural cells in response to said neurons firing together;decrease activity at the location of interest by inducing long-termdepression (LTD); long-lasting reduction in signal transmission thatoccurs between neurons in response to certain patterns of stimulation(such as repetitive stimulation at one pulse per second for durations of15 minutes); or improve the availability of physiological resources tothe neural tissue by increasing local cerebral blood flow (CBF). Thegoal may be selected based on an assumption that electrical stimulationcharacterized by certain parameters is likely to be effective inachieving the goal. The parameters associated with these goals arediscussed in more detail below.

In one example, a goal of the electrical stimulation therapy may bedetermined to decrease neuronal activity by producing a depolarizationor conduction block that blocks neuronal firing. If the electricalstimulation consists of pulses delivered at high frequency such as at orabove 100 Hz (at or below a 10 ms inter-pulse interval 524), andmoderate burst durations such as 100 to 1000 ms and inhibition of neuralactivity at the location of interest or at a location that receivesexcitatory projections from or through the location of interest isdeemed likely to be beneficial to the patient, then the goal ofstimulation may be categorized as “depolarization block”. Suchinhibition may be judged to be beneficial to the patient if, forinstance, symptoms of a neurological disorder are associated with excessexcitation of the location of interest or a region that receivesexcitatory projections from or through that location. An example ofstimulation that might be expected to achieve a “depolarization block”goal would be stimulation of the hippocampus in epilepsy using 250 Hzpulses with burst duration 200 ms.

In another example, a goal of stimulation may be to increase activity ata location of interest or increase outflow of a neurotransmitterproduced by a location of interest by directly causing firing of actionpotentials at that location, or to increase activity at a differentregion other than the location of interest by causing cells to fire thathave substantially excitatory projections to said different region. Ifthe electrical stimulation consists of pulses delivered at low frequencysuch as 1 to 50 Hz and long burst durations such as 1 second or above,and excitation of neural activity at the location of interest or saiddifferent region is deemed to be beneficial to the patient, then thegoal of stimulation may be categorized as “excitation.” Such excitationmay be judged to be beneficial to the patient if, for instance, symptomsof a neurological disorder are associated with excess inhibition,inadequate plasticity, or inadequate excitation at the location ofinterest or said different region. An example of stimulation that mightbe expected to achieve an “excitation” goal would be stimulation of theipsilateral motor cortex in stroke using 50 Hz pulses with burstduration 1 sec.

In yet other examples, a goal of stimulation may be to decrease activityat a location of interest by directly causing firing of actionpotentials in inhibitory neurons, such as interneurons, at the locationof interest, or to decrease activity at a different region other thanthe location of interest by causing cells to fire that havesubstantially inhibitory projections to said different region. If theelectrical stimulation consists of pulses delivered at high frequenciesthat tend to selectively stimulate interneurons such as 150 to 250 Hz,and moderate burst durations such as 100 to 1000 ms, and inhibition ofneural activity at the location of interest is beneficial to thepatient, then the goal of stimulation may be categorized as“inhibition.” If stimulation consists of pulses delivered at moderatefrequencies such as 1 to 50 Hz and long burst durations such as 1 sec orabove, and inhibition of neural activity at said different region isdeemed to be beneficial to the patient, then the goal of stimulation maybe also categorized as “inhibition.” Such inhibition may be judged to bebeneficial to the patient if, for instance, symptoms of a neurologicaldisorder are associated with excess excitation of the location ofinterest or a region that receives inhibitory projections from orthrough that location. Examples of stimulation that might be expected toachieve an “inhibition” goal include stimulation of the external globuspallidus (GPe) in Parkinson's disease using 50 Hz pulses with burstduration 1 sec in order to cause inhibition of the subthalamic nucleus(activating the inhibitory projections from the GPe to the subthalamicnucleus), or stimulation at a seizure focus in epilepsy using 200 Hzpulses with burst duration 200 ms to cause firing of local inhibitoryinterneurons.

In still another example, a goal of stimulation may be to increaseactivity or plasticity at a location of interest by inducing LTP. If theelectrical stimulation consists of pulses delivered in a manner known tocause LTP, such as pulses at 50 Hz or groups of three pulses at 100 Hzdelivered at one group every 200 ms (known as theta burst stimulation),and excitation of neural activity or increased plasticity at thelocation of interest is deemed to be beneficial to the patient, then thegoal of stimulation is categorized as “LTP induction.” Such excitationor plasticity may be judged to be beneficial to the patient if, forinstance, symptoms of a neurological disorder are associated with excessinhibition, inadequate excitation, or inadequate plasticity at thelocation of interest. An example of stimulation that may be expected toachieve an “LTP induction” goal includes stimulation of the ipsilateralmotor cortex in stroke using theta burst stimulation.

In a further example, a goal of stimulation may be to decrease activityat a target region by inducing LTD. If the electrical stimulationconsists of pulses delivered in a manner known to cause LTD, such aspulses at very low frequencies such as long burst durations 536 (15minutes) at 1 Hz, and inhibition of neural activity at the target regionis deemed to be beneficial to the patient, then the goal of stimulationmay be categorized as “LTD induction.” Such inhibition may be judged tobe beneficial to the patient if, for instance, symptoms of aneurological disorder are associated with excess excitation or excessactivity at the location of interest. An example of stimulation that maybe expected to achieve an “LTP depression” goal includes stimulation ofa seizure focus in epilepsy using 1 Hz stimulation.

In a still further example, a goal of stimulation can be to improveavailability of physiological resources to the neural tissue byincreasing local cerebral blood flow (CBF). If the electricalstimulation consists of pulses delivered in a manner known to increaselocal CBF, such as pulses at moderate to high frequencies such as 50 to200 Hz delivered in moderately long bursts such as 100 to 1000 ms, andincreased local CBF at the location of interest is deemed to bebeneficial to the patient, then the goal of stimulation may becategorized as “CBF increase.” Such CBF increase may be judged to bebeneficial to the patient if, for instance, symptoms of a neurologicaldisorder are associated with impaired neurovascular coupling or reducedavailability of physiological resources such as oxygen or glucose at thelocation of interest. An example of stimulation that may be expected toachieve a “CBF increase” goal includes stimulation of a seizure focus inepilepsy using 100 Hz stimulation delivered in 200 ms bursts separatedby 800 ms or more elapsed time between bursts.

Other goals for stimulation may be determined than are mentioned above,for example, based on research that suggests a certain type ofelectrical stimulation is likely to have a beneficial effect on neuronsinvolved in a certain way with a certain neurological disorder. For agiven combination of therapies (electrical stimulation and drug and/orsome other therapy), more than one goal may be determined. Thus, thereoften may be a need to prioritize goals of a particular combinationtherapy, so that, for example, only one goal will be selected forfacilitating with electrical stimulation and a drug therapy at a time.Further, one or more goals of a combination of therapies may change overtime based, for example, on changes in the condition of the patient ornew information about the mechanism by which electrical stimulationeffects a neural circuit or the mechanism by which a drug functions atthe molecular level.

Once a patient's physician has determined a goal, the physician shouldconsider whether attempts to achieve that goal might result inundesirable effects as well as effects consistent with the goal.

For example, a physician may choose a stimulation goal of excitation forthe stimulation location. However, the stimulation may activate not onlythe neurons of interest but also some of the neurons in or near orotherwise functionally associated with the stimulation locations. Ifsuch excitation is inconsistent with the goal of the electricalstimulation, then it may be considered an undesirable effect.

For example, a physician may wish to increase the activity of inhibitoryinterneurons at the stimulation location. However, the stimulationparameters used to increase the activity of the inhibitory cells mayalso increase the activity of excitatory neurons. Activation ofexcitatory neurons by electrical stimulation may be considered to bedetrimental to the patient if, for instance, the excitation effectcauses symptoms of a neurological disorder to worsen or tend to undo aclinical benefit the patient otherwise was experiencing (either frompre-existing electrical stimulation or a drug regimen or somecombination of both). An example of a circumstance in which excitationof inhibitory interneurons may be chosen as a goal would be thetreatment of epilepsy by electrical stimulation at the seizure focus.However, in this circumstance excitation of excitatory neurons at theseizure focus would be deemed to be undesirable and would result inexcitation of the seizure focus and thus a potential seizure. Thisundesirable effect of stimulation may be mitigated by choosing anappropriate drug therapy allowing the positive effect of stimulation(excitation of inhibitory neurons) and minimizing the undesirable effect(excitation of excitatory neurons).

By way of further example, a physician may select the goal of excitationand may intend to use stimulation to increase excitatory activity whenthe stimulation waveform is delivered to a location(s) of interest.However, similar to the example above the same stimulation waveform mayactivate both excitatory neurons at the location of interest andinhibitory neurons in or near or otherwise functionally associated withthat location. Thus the net effect of stimulation may be inhibitoryinstead of excitatory. An example of a circumstance in which aninhibition effect would be deemed to be undesirable would be whenelectrical stimulation inhibits a patient's motor cortex due toexcitation of local inhibitory connections in direct corticalneurostimulation, where the direct cortical stimulation is beingdelivered to facilitate stroke rehabilitation. Thus using a drug ordrugs that enhance the effect of stimulation on excitatory neurons andminimize the effect of stimulation on inhibitory neurons may bebeneficial in order to facilitate stimulation therapy for strokerehabilitation.

Referring again to FIG. 14, and as indicated by the flow chart block1430, if a patient's treating physician decides after weighing the prosand especially the potential cons associated with a particular goal,that the risk associated with the potential cons can be mitigated, thenthe physician can select a drug or drugs in an effort to facilitate theparticular goal and/or to prevent or inhibit the undesirable effect oreffects of stimulation.

For example, a physician may select a medication in the class of drugsknown as “ion channel blockers” in an effort to facilitate the effect ofan electrical stimulation therapy associated with a “depolarizationblock” goal in the treatment of epilepsy or migraine.

In another example, a physician may select a medication with multiplemechanisms of action such as felbamate, which acts to both increase theresponse to inhibitory neurotransmitters and decrease the response toexcitatory neurotransmitters in an effort to facilitate the effect of anelectrical stimulation therapy which is associated with a goal of“increasing neurotransmitter release” for the treatment of epilepsy.

As mentioned above, this type of stimulation goal may result in thenonspecific increase of both excitatory and inhibitoryneurotransmitters. If the intention of treatment is to increaseinhibitory neurotransmitter release the stimulation induced increase ofexcitatory neurotransmitter release may be an undesired effect ofstimulation. Since felbamate has multiple mechanisms of action andenhances the effect of the inhibitory neurotransmitter while reducingthe response to excitatory neurotransmitters combining felbamate withthis type of stimulation therapy would enhance the goal of stimulationand minimize the undesirable effect of stimulation. Thus combiningstimulation to increase neurotransmitter release with a drug such asfelbamate may produce the desired net inhibitory response for treatingseizures at the epileptic focus.

By way of still further example, a physician may select a medication inthe class of drugs known as “inhibitory neurotransmitter receptorpositive modulators”, such as a benzodiazepine, in an effort tofacilitate the effect of an electrical stimulation therapy which isassociated with a goal of “inhibition” to treat a patient with epilepsy.

In yet another example, a physician may select a medication in the classof drugs known as “serotonin reuptake inhibitors (SSRI)”, in an effortto facilitate the effect of an electrical stimulation therapy which isassociated with a goal of “excitation” to treat a patient suffering fromMajor Depressive Disorder (“MDD”). Excitation will increase neuralactivity which will result in increased neurotransmitter release,including increased serotonin release, which is desirable in treatingdepression. SSRIs would be expected to enhance the effect of stimulationby decreasing the rate at which serotonin is removed from the synapse.

In some embodiments, one or more of determining a goal of an electricalstimulation therapy (as indicated by the flow chart block 1410);evaluating the potential undesirable effects of particular electricalstimulation parameters or parameter values for the therapy relative tothe goal (as indicated by the flow chart block 1420); choosing a drugregimen in light of the stimulation goal and the evaluation of thestimulation parameters (as indicated by the flow chart block 1430); andstarting the patient on a drug regimen or adjusting the patient's drugregimen (as indicated by the flow chart block 1440), may be assisted orcarried out in part or entirely by one or more of the externalcomponents (such as the programmer or patient remote monitor 362 or thedata management system 360) and/or based at least in part on dataacquired from a patient using an implantable medical device 100 and/ordata associated with a condition or conditions of the implantablemedical device 100 (e.g., a count of the number of “detections per day”or the instances of saturation of an amplifier of the implantablemedical device 100).

Moreover, once a combination of an electrical stimulation therapy and adrug therapy has been decided upon, monitoring the subsequent responseof the patient to the combination therapy may be accomplished using theimplantable medical device 100 in conjunction with the sensing elements342, sensing/stimulation elements 340, and stimulation elements 344(such as the electrode-bearing leads 114, 116) together with one or moreof the external components such as the programmer or patient remotemonitor 362 and/or the data management system 360.

As a result of such monitoring, the physician or some component of asystem automatically may adjust one or more parameters of a drug regimen(e.g., dosage adjusted, medication added, medication removed, etc.) inan effort to improve the patient's overall response or to react to achange in prioritization of one or more of the goals. The automaticadjustment may comprise an output defining the changed drug regimen andthus may require some action by the patient in order to be carried out,such as the patient taking a different pill. Alternatively, theautomatic adjustment may comprise commanding an implanted drug deliverydevice to deliver a new drug or change the dose of a drug already in thepatient's drug regimen. (A medication may be prescribed by a physicianor and delivered to the patient using delivery methods such as tablets,capsules, injection, or drug-eluting or drug-releasing electrodes orimplants.) Similarly, the parameters according to which electricalstimulation therapy is delivered also may be modified or adjustedautomatically in whole or in part, for example reprogramming a set ofstimulation parameters as commanded via a programmer 362 by a physician.

FIG. 15 is a flowchart of a method according to embodiments forselecting one or more medications to facilitate the desirable effects ofan electrical stimulation therapy generated by, for example, animplantable medical device 100 described elsewhere herein configured asa neurostimulator. The stimulation may be delivered to the patientthrough one or more stimulation pathways configured using theimplantable medical device 100 and one or more of the stimulationelement 344 and sensing/stimulation element 340.

A goal for an electrical stimulation therapy is determined (as indicatedby the flow chart block 1510). Based on the goal, a class of drug isselected.

For example, and as is indicated by the flow chart block 1520, if thegoal is “depolarization block”, then a sodium channel blocker such asphenytoin or carbamazepine is selected (as is indicated by the flowchart block 1522).

If, and as is indicated by the flow chart block 1530, the goal is“excitation,” then a drug in the class of any of a depolarizing agent,an agonist, or a reuptake inhibitor is selected (as indicated by theflow chart block 1532). More specifically, the medication may be onethat tends to depolarize neural tissue such as cholecystekinine or amedication such as a serotonin reuptake inhibitor (SSRI) that tends toenhance effects of a neurotransmitter whose release is caused byneurostimulation is selected.

If, and as indicated by the flow chart block 1540, the goal is“inhibition”, then a drug in the class of GABAergic agonist is selected(as indicated by the flow chart block 1542). For example, the medicationselected may be a benzodiazepine that potentiates an inhibitoryneurotransmitter such as GABA.

If, and as indicated by the flow chart block 1550, the goal is “longterm potentiation (LTP) induction,” then a drug in the class of any ofan agonist or LTP enhancer is selected (as indicated by the flow chartblock 1552). For example, the medication selected may be one thatfacilitates LTP by increasing BDNF (brain-derived neurotrophic factor)such as venlafaxine, or acts as a nicotinic acetylcholine receptoragonist such as galantamine is selected.

If, and is indicated by the flow chart block 1560, the goal is “longterm depression (LTD) induction”, then a drug in the class of any of anantagonist or an LTD enhancer is selected (as indicated by the flowchart block 1562). For example, the medication selected may be a D2receptor blocker such as clozapine or a medication that inhibitsglutamate uptake such as tamoxifen.

Finally, and as indicated in the flow chart block 1570, the goal is“cerebral blood flow (CBF) increase,” then a drug in the class ofvasodilators is selected (as indicated by the flow chart block 1572).For example, the medication selected may be a medication that causes anincrease in CBF such as a diuretic, for example furosemide, or axanthine derivative such as pentoxifylline.

FIG. 16 is a flowchart of a method according to embodiments forselecting one or more medications to mitigate the risk that potentialundesirable effects of a candidate electrical stimulation therapy willoccur when the stimulation therapy is delivered to a patient using, forexample, an implantable medical device 100 described elsewhere hereinconfigured as a neurostimulator.

Referring initially to block 1610 of the flow chart of FIG. 16, thepotential undesirable effect of a candidate electrical stimulationtherapy is determined.

If the potential undesirable effect of the candidate electricalstimulation therapy is “undesirable excitation” as indicated in block1620, then a drug in the class of any of a glutaminergic antagonist, aGABAergic agonist, and a sodium channel (Na+) blocker is selected (atblock 1630). Drugs in these classes tend to reduce neural excitation orneural firing.

If the potential undesirable effect of the candidate electricalstimulation therapy is “undesirable inhibition” as indicated in block1640, then a drug in the class of any of a glutaminergic agonist, aGABAergic agonist, and a sodium channel (Na+) blocker is selected (atblock 1650). Drugs in these classes tend to decrease unwanted fastfiring of inhibitory neural tissue.

In other embodiments where a combination of therapies is delivered to apatient and it is desirable to exploit synergies among the therapies andminimize antagonisms, systems and methods are described in which thefine tuning of the combinations of therapies is accomplished at least inpart automatically, such as by using an implantable medical device 100,as will be described in more detail below.

More particularly some embodiments of a system and methods rely uponpredictable and/or predetermined relationships between a patient'sresponse to a drug regimen and the patient's response to electricalstimulation therapy, as is described below. For example, in the presenceof specific medications, a patient's response to neurostimulation may beimproved by adjusting specific stimulation parameters in a predictableand predetermined fashion.

More specifically, in the presence of sodium channel blockers such asphenytoin or carbamazepine, a patient's response to stimulation oftenmay be improved by increasing the burst duration 536, 538, such as by100 ms increments with a start point of 100 ms and not exceeding 1second. Increasing the burst duration 536, 538 makes it more likely thatdepolarization and/or conduction blocks will be created, and might beexpected to produce a neuronal response similar to and synergistic withthat produced by sodium channel blockers (which sodium channel blockersinhibit high frequency repetitive neuronal firing).

FIG. 17 is a flowchart of an embodiment for selecting neurostimulationparameters in treatment of partial onset epilepsy to maximizeeffectiveness of a combined therapy comprising the neurostimulationtherapy and a drug therapy.

At the block 1710 in the flow chart of FIG. 17, a mechanism of action isdetermined (or assumed or predicted) for a medication that a patienteither is already taking or which the physician is considering adding toa patient's drug regimen. By way of example and not by way oflimitation, a drug may be characterizable by a primary mechanism ofaction, multiple mechanisms of action, or an SV2A mechanism of action.

Examples of a drug with a primary mechanism action of a drug include“sodium channel blockers” (the drugs phenytoin or carbamazepine areincluded in this class of drugs) and “GABA agonists” (barbiturates andbenzodiazepines are included in this class of drugs). Drugs associatedwith multiple mechanisms of action include felbamate which acts as botha glutamate receptor antagonist and a GABA receptor positive modulator.Drugs with a mechanism of action that modulates the activity of synapticvesicle protein 2A (SV2A) include levetiracetam.

Typically, where a drug is susceptible of more than one mechanism ofaction, embodiments of the system and method described herein willendeavor to encourage only one such mechanism of action at a time. Someantiepileptic medications in each class are set forth in Table 1.0below.

Antiepileptic Medication Adult Daily Dose GABA agonists — clonazepam1.5-20 mg gabapentin 900-3600 mg phenobarbital 60-200 mg pregabalin150-600 mg tiagabine 36-56 mg vigabatrin 1-3 g Sodium channel blockers —carbamazepine 600-1400 mg lacosamide 200-600 mg oxcarbazepine 600-2400mg phenytoin 200-400 mg Multiple mechanisms — felbamate 1200-3600 mglamotrigine 100-500 mg primidone 250-1000 mg topiramate 200-400 mgvalproate/valproic acid 1000-6500 mg zonisamide 100-600 mg Other —levetiracetam 1000-3000 mg ethosuximide 500-1500 mg

Whether the medication is a sodium channel blocker is determined at theblock 1720 in the flow chart of FIG. 17. If the medication is a sodiumchannel blocker, then a parameter in the set of stimulation parametersdefining a burst duration 536, 538 may be increased (at block 1722). Forexample, the burst duration may be increase in 100 ms increments until aburst duration 536, 538 of one second is reached, and/or the burstduration parameter may be associated with a not-to-exceed limit of onesecond. Alternatively or additionally, the frequency of pulses 510 beingdelivered to the patient in a stimulation waveform may be increased (atblock 1722), for example, in 5 Hz increments until a frequency of 250 Hzis reached, and/or the frequency parameter may be associated with anot-to-exceed upper limit of 250 Hz. It will be appreciated that, thepatient's response to the incremental changes in the frequencyparameters can be monitored by repeatedly measuring physiological dataat the stimulation location in the brain as described in more detailabove and as described with reference to FIGS. 7-12.

Whether the medication is a GABA or glutamate modulator is determined atthe block 1730 in the flow chart of FIG. 17. If the medication is a GABAor glutamate modulator, then a parameter in the set of stimulationparameters defining a burst duration 536, 538 may be increased (at block1732). For example, the burst duration may be increase in 200 msincrements until a burst duration 536, 538 of one second is reached,and/or the burst duration parameter may be associated with anot-to-exceed limit of one second. Alternatively or additionally, thefrequency of pulses 510 being delivered to the patient in a stimulationwaveform may be decreased (at block 1732), for example, in 5 Hzincrements until a frequency of 1 Hz is reached, and/or the frequencyparameter may be associated with a not to exceed lower limit of 1 Hz andto be below a lower limit of 50 Hz.

Whether the medication has a mixed mechanism of action is determined atthe block 1740 in the flow chart of FIG. 17. If the medication has amixed mechanism of action, then a parameter in the set of stimulationparameters defining a burst duration 536, 538 may be decreased (at block1742). For example, the burst duration may be decreased in 50 msincrements until a lower burst duration 536, 538 threshold of 100 ms isreached, and/or the burst duration parameter may be associated with anot-to-fall-below limit of 100 ms. Alternatively or additionally, thefrequency of pulses 510 being delivered to the patient in a stimulationwaveform may be decreased (at block 1742), for example, in 5 Hzincrements until a frequency of 100 Hz is reached, and/or the frequencyparameter may be associated with a not-to-exceed lower limit of 100 Hz.

Whether the medication has the mechanism of action constitutingmodulating the activity of synaptic vesicle protein 2A (SV2A) isdetermined at the block 1750 in the flow chart of FIG. 17. If themedication has the “SV2A” mechanism of action, then a parameter in theset of stimulation parameters defining a stimulation amplitude 518 maybe increased (at block 1752), such as by increasing a stimulationvoltage in 0.1 mA increments. Alternatively or additionally, a phasewidth parameter (516, 518) may be increased (at block 1752), forexample, in 40 μs increments.

After one or more of the stimulation parameters are adjusted accordingto any of the actions represented by the blocks 1722, 1732, 1742, 1752,further assessment of a medication may be undertaken (at the block 1760)to determine whether any mechanism of action of a drug is dependent onthe cerebral blood flow (CBF) in a particular location(s) of interest ofthe patient's brain (for example, in the pathway defined by one or morestimulation elements 344 or at a sensing element 342). If a mechanism ofaction of a drug is dependent on CBF, then it may be inferred that thetherapeutic efficacy will vary with the cerebral blood flow. Forexample, it may be inferred that the therapeutic efficacy of a givendrug whose mechanism of action depends on local cerebral blood flow willdecrease when the local cerebral blood flow decreases.

In circumstances where local cerebral blood flow is presumed to have aneffect on the therapeutic efficacy of a drug, then rather than merelyadjusting parameters according to which a given stimulation waveform isbeing delivered, embodiments may introduce a new stimulation waveform tothe stimulation therapy. For example, the new stimulation waveform maybe the same or different in kind (e.g., may be characterized by the sameset of stimulation parameters as an existing stimulation waveform orwaveforms, or it may be characterized by a different set of stimulationparameters as an existing waveform or waveforms). Alternatively oradditionally, a new stimulation waveform may be generated and output byan implantable medical device 100 and delivered through a differentstimulation element 344 or stimulation elements, so that a differentlocation of interest of the brain or different functional circuit of thebrain is stimulated. The new stimulation waveforms may be intended toencourage the local cerebral blood flow to increase so as to increasethe therapeutic efficacy of a drug in the patient's drug regimen. In aparticular example, a new stimulation waveform may be generated andoutput by an implanted medical device 100 configured as aneurostimulator with a frequency of 100 Hz stimulation delivered in 200ms bursts separated by 800 ms elapsed time between bursts. Further, theimplantable medical device 100 configured as a neurostimulator may beprogrammed or otherwise instructed to deliver the new stimulationwaveform to a stimulation pathway (e.g., formed between one or morestimulation elements 344 or between one or more stimulation elements 344and the neurostimulator) to treat a location in a patient's brain thatis believed to constitute a seizure focus for that patient.

After any further assessments are made to determine information aboutlocal cerebral blood flow (i.e., the actions represented by the blocks1760 and 1762 in FIG. 17) and after one or more of the stimulationparameters are adjusted according to any of the actions represented bythe blocks 1722, 1732, 1742, 1752, then a still further assessment of amedication may be undertaken (at the block 1770) to determine whetherany mechanism of action of a drug is dependent on local cellularactivity (such as a level of neural activity). If a mechanism of actionof a drug is dependent on local cellular activity, then it may beinferred that the therapeutic efficacy will vary with variations in thelocal cellular activity. For example, it may be inferred that thetherapeutic efficacy of a given drug whose mechanism of action dependson local cellular activity will decrease when the local cellularactivity decreases.

An example of a medication that is understood to have an effect on localcellular activity is 2-deoxy-D-glucose (2-DG).

In circumstances where local cellular activity is presumed to have aneffect on the therapeutic efficacy of a drug, then (and as is the casewhen local cerebral blood flow is presumed to have an effect on thetherapeutic efficacy of a drug) rather than merely adjusting parametersaccording to which a given stimulation waveform is being delivered,embodiments may introduce a new stimulation waveform to the stimulationtherapy. The new stimulation waveform may be one of the stimulationwaveforms described above in connection with the block 1760 and 1762 ofFIG. 17.

In a particular example, a new stimulation waveform may be generated andoutput by an implanted medical device 100 configured as aneurostimulator with a frequency of 50 Hz stimulation delivered in onesecond bursts separated by 5000 ms or more elapsed time between bursts.Further, the implantable medical device 100 configured as aneurostimulator will be programmed or otherwise instructed to deliverthe new stimulation waveform to a stimulation pathway (e.g., formedbetween one or more stimulation elements 344 or between one or morestimulation elements 344 and the neurostimulator) to treat a location ina patient's brain that is believed to constitute a seizure focus forthat patient.

It should be appreciated that additional or further assessments of amechanism of action of a drug (including but not limited to mechanismsof action that are affected by local cerebral blood flow or localcellular activity) may be made each time or on predetermined basis orotherwise scheduled after a change to one or more stimulation parametershas been made. Such additional or further assessments may beaccomplished to monitor the effect of a change in the short or long termin an effort to maintain a beneficial overall response of the patient tothe combination of therapies.

Similarly, assays of the concentrations of a drug in the patient andother physiological data (including neurochemical measurements) may beacquired from the patient from time to time, automatically through use,for example, of the implantable medical device 100, by a physician orlaboratory worker in a clinical setting, or some combination of some orall of the implantable medical device 100, an external component such asthe programmer or remote monitor 362 or the data management system 360,and the patient's physician. Of course, if the additional or furtherassessments or assay or other acquired physiological data suggest that apatient is no longer responding beneficially to a particular combinationtherapy, then appropriate changes to the patient's treatment may bemade.

It should further be appreciated that embodiments including the generalprinciples of making adjustments to stimulation parameters andstimulation waveforms while a patient is receiving a drug therapy may beapplied in a wide variety of circumstances. For example, combinationtherapies and the adjustment thereof as described herein may be appliedto many different disorders of the nervous system.

Referring now to FIGS. 18-21, described are embodiments of systems andmethods in which one or more parameters of a combination therapyincluding at least a drug therapy and an electrical stimulation therapymay be adjusted in an effort to control the overall result of thecombination therapy. The adjusting may be carried out automatically,such as autonomously by an implantable medical device 100 coupled to oneor more sensing/stimulation elements 340, sensing elements 342 andstimulation elements 344 in part-time (including in real-time)communication with one or more host devices, including one or moreexternal components such as the programmer or patient remote monitor 362or the data management system 360. Alternatively or additionally, theadjusting may be carried out at least in part automatically by one ormore implanted or external components operating alone or together withinput from the patient's treating physician.

The adjusting may be based on variables including, but not limited toany of the following: (1) the parameters defining a drug regimen towhich the patient is currently being subjected; (2) the patient'shistory of drug regimens and changes thereto; (3) the dosage of a drugthat is might be toxic to the patient (either when taken alone or incombination with other drugs or in view of certain behaviors of thepatient (e.g., smoking, alcohol consumption); (4) an electricalstimulation therapy the patient is currently receiving; (5) thepatient's history of electrical stimulation therapies and changesthereto; (6) data concerning drug regimens and electrical stimulationtherapy experience for patients falling within the same group ordemographic as the patient; (7) physiological data (such aselectrographic signals, neurochemical concentrations, oxygenationconcentrations, pressure and temperature measurements, accelerometermeasurements and so on and so forth); (8) conditions of a device thatacquires the physiological data (such as the number of saturations orthe length of a saturation of a sensing amplifier in an implantablemedical device 100 configured to process and analyzed the physiologicaldata sensed from the patient; the occurrences of predetermined “detectedevents” an implantable medical device is configured to recognize in theacquired physiological data, or the occurrences of some other identifiedcharacteristics the implantable medical device is configured torecognize in the acquired physiological data); and (9) a “goal” ofstimulation therapy (as described above with reference to FIG. 14)

The adjusting may be accomplished in a feedback loop in order tomaintain an output of a system relative to a target. The target may be adiscrete value, a not-to-exceed value (such as a fixed or dynamicthreshold), or a range of values.

FIG. 18 is a flow chart for embodiments of a system and method foroptimizing the parameters according to which electrical stimulationtherapy is delivered to a patient in combination with a drug therapy,based on known information about the parameters of a drug regimen towhich the patient is being subjected.

Preliminarily, it is assumed that a neurostimulator already has beenconfigured for the patient receiving the drug regimen; preferably, animplantable medical device 100 configured as a neurostimulator accordingto a set of programmable and variable stimulation parameters. The set ofstimulation parameters, for example, may govern the number andcomposition of the stimulation pathways (e.g., which stimulationelectrodes are used) for delivering one or more stimulation waveforms,the timing for delivering of each stimulation waveform (e.g.,continuously, periodically on a scheduled basis, or in response to theoccurrence of a predetermined trigger), as well as the number andcomposition of the stimulation waveforms themselves and the timing fordelivering of each stimulation waveform.

Typical parameters for stimulation waveforms include the type ofwaveform (e.g., pulsatile or sine wave or “near-DC”), whether thewaveform is characterized by a duty cycle when the stimulation is “on”for a part of the duty cycle and “off” for another part of the dutycycle, the morphology of the waveform (e.g., shape of pulses or shape ofbursts), the number of pulses, the pulse parameters (e.g., amplitude,phase width, inter-phase interval, inter-pulse interval (the inverse ofwhich is frequency), the burst parameters (e.g., number of pulses in aburst, whether a burst has “ramp up” period and/or a “ramp down”period), etc.

In some embodiments, the parameters with which an implantable medicaldevice 100 has been configured (e.g., the neurostimulator or anotherimplantable medical device in operable communication with theneurostimulator) may include a set of detection parameters. For example,when the neurostimulator may be configured to deliver stimulationwaveforms when certain predetermined features or elements are recognizedin the physiological data sensed from one or more sensing elements 342(i.e., in a “responsive neurostimulation” implementation of aneurostimulation system). The predetermined features or elements may bedefined as characteristics to identify in a sensed signal or measurementor “events” to “detect” in the acquired physiological data.

The set of detection parameters or some other parameters that governoperation of the implantable neurostimulation system may cause portionsof the acquired physiological data (or digital representations or otherapproximations thereof) to be recorded by the implantable medical device(e.g., in a recording module 320) and/or by some other component of theneurostimulation system, such as an external component comprising aprogrammer or patient remote monitor 362 or a data management system360.

The set of detection parameters or some other parameters that governoperation of the implantable neurostimulation system also may cause datato be stored about one or more conditions of the implantable medicaldevice whenever an identified characteristic or detected event occurs(such as in an event counting/logging module 322 of the implantablemedical device 100 or in some other implantable or external component ofa neurostimulation system). These device conditions may include but arenot limited to data items such as the date and time when an identifiedcondition or detected event occurs and whether the condition or eventwas associated with a change in the device (e.g., saturation of asensing amplifier).

Referring now to block 1810 of FIG. 18, a patient's physician or otheruser provides information relating to the parameters of the current drugregimen of the patient as an input to embodiments of the system ormethod. The parameters of a drug regimen may include but are not limitedto: the number and type of drugs being used (e.g., three drugs total thethree drugs being carbamazepine, felbamate, and fluoxetine); the classor mechanism of action of each drug (e.g., sodium channel blocker (onemechanism of action), GABA receptor positive modulator and glutamatereceptor antagonist (two mechanisms of action), selective serotoninreuptake inhibitor (SSRI) (one mechanism of action); the dosage of eachdrug; the timing according to which a total (e.g., daily) dose isachieved; and the method by which each drug is delivered (e.g., orallyingested, injected, delivered using an implanted drug delivery elementor system, etc.). The drug regimen or drug regimens to which a patientis subjected may be referred to herein as a “medication environment.”

As indicated in block 1820 of FIG. 18, one or more components determineone or more control algorithm to use for deciding whether and, if so,when to adjust parameters in a set of stimulation parameters, based inpart on the medication environment. Also at block 1820, one or morecomponents determine a target or targets to associate with thecombination therapy.

The control algorithm may be selected from a set of previously definedcontrol algorithms or the control algorithm may be developed accordingto one or more rules that the system and method may access (e.g., rulesthat are made available from a central processing unit of theimplantable medical device 100, or from some other host, such as hostconfigured as one of the external components (e.g., the programmer orpatient remote monitor 362 or the data management system 360), a hostconfigured as a different implantable medical device, or a hostconfigured using a combination of implantable devices or components andexternal devices or components.

A target may be associated with, for example, one or more desiredtherapeutic outcomes, with some sort of calibration of the overallsystem, or with a safety limit or safety margin within which the systemis intended to operate. A target may comprise a discrete value, athreshold (e.g., a fixed threshold or a dynamic threshold that variesbased on a trend or a predetermined relationship with the value of someother variable in the system), a range of values (e.g., a range of about50 Hz to about 250 Hz for a parameter corresponding to the frequencywith which stimulation pulses 510 are delivered to a patient in a givenstimulation waveform). Embodiments may be configured to determinetargets based on a look up table or by using one or more algorithms orcalculations based on, for instance, system knowledge of the medicationenvironment and existing or historical stimulation parameter values.

After the medication environment is established (at block 1810), and thecontrol algorithm(s) and target(s) are determined (at block 1820), thesystem and method acquire, process and analyze physiological data andcompare the results of the analyses to the relevant target(s) in orderto assess whether the target(s) is/are met. The system and method mayacquire, process, and analyze the physiological data in any of the wayspreviously described herein. For example, the physiological data maycomprise electrographic signals sensed from desired sensing locations inthe patient's brain, and the processing may include filtering thesignals to reduce noise and converting the signals from an analog formto a digital form, and the analyzing may include identifying how much ofthe power of the signal falls within a certain frequency band and whenthere is a predetermined amount of power in that frequency band,recognizing a “detected event.” Alternatively or additionally, thephysiological data may comprise a measure of the concentration of aneurochemical in the tissue at or near a sensing element 342.

If the system and method deem a target associated with the analyzedphysiological data to have been met (at block 1840), then the system andmethod may wait a period of time corresponding to a “delay-after-targetmet” time, as indicated at block 1870 in FIG. 18, before the system andmethod again acquires, processes and analyzes the physiological datarelevant to that target. In some embodiments, the“delay-after-target-met” time may be a variable that is programmablewithin a predetermined range. For example, the “delay-after-target-met”time may be programmable from one to 5 days. The“delay-after-target-met” time may be selected based on other criteriathat affect operation of the system. In some circumstances where theacquiring, processing and analyzing of the physiological data relies ona power source contained within the implantable medical device 100(e.g., a primary cell or rechargeable battery), how often thephysiological data is re-analyzed after a given target has been met maybe dictated in part by how much power a measurement consumes or what isthe capacity of the power source. In a particular instance, the“delay-after-target-met” time may be three days.

If the system and method deem a target associated with the analyzedphysiological data not to have been met (at block 1840), then the systemand method may adjust one or more of the parameters according to whichthe electrical stimulation therapy is delivered. The controlalgorithm(s) developed at block 1820 may determine which stimulationparameters are adjusted and how they are adjusted. For a givenadjustment at block 1860, a single one (e.g., burst duration) ormultiple ones (e.g., amplitude and frequency) of the stimulationparameters may be modified.

Following any parameter adjustment at block 1860, the system and methodmay again, at block 1830, acquire, process, and analyze thephysiological data and compare it again to the relevant target to assesswhether the adjustment had the desired result (e.g., whether theadjustment does or does not result in targets being met). In someembodiments, following parameter adjustment at block 1860 and beforeagain acquiring, processing and analyzing the physiological data atblock 1830, the system will wait for a period of time corresponding to a“delay-after-parameter-adjustment” time, as indicated at block 1870 inFIG. 18. In some embodiments, the “delay-after-parameter-adjustment”time may be a variable that is programmable within a predeterminedrange. For example, the “delay-after-parameter-adjustment” time may beprogrammable from one to 24 hours. The“delay-after-parameter-adjustment” time may be selected based on othercriteria that affect operation of the system. In some circumstanceswhere the acquiring, processing, and analyzing of the physiological datarelies on counting or logging a number of “detections per day”, then the“delay-after-parameter-adjustment” time may be set for at least a day sothat the effect an adjustment has on the “detections per day” can beappreciated by the system and method. Alternatively or additionally, a“delay-after-parameter-adjustment” time may be selected to allow thepatient's nervous system to equilibrate or stabilize or otherwise becomeacclimated or accustomed to the combination therapy delivered accordingto the adjusted (e.g., new or modified) stimulation parameters.

In embodiments in which parameter adjustment is accomplishedautomatically by a host device while the host device is in communicationwith an implantable neurostimulator, such as a host device comprising orincluding an external component such as the programmer or patient remotemonitor 362 or the data management system 360, the host deviceaccomplishing the adjustment would first retrieve the informationacquired, processed, and analyzed by the implantable medical device 100from the implantable medical device or from a location where theinformation previously has been stored on an external device (such as ina memory of a programmer or patient remote monitor 362 or a database ofthe data management system 360), develop the control algorithm(s), testthe physiological data information against the target(s), and identify(using the control algorithm(s) and targets) what, if any, adjustmentsto the stimulation parameters should be made, and then transmit (eitherimmediately or whenever a communication link is next established withthe implanted components) any parameter adjustments for the implantableneurostimulator system's use in generating, outputting, and deliveringstimulation according to the relevant set of parameters, as adjusted.

In other embodiments, a data management system 360 may retrieve theinformation acquired, processed and analyzed by the implantable medicaldevice, develop the control algorithm(s), test the physiological datainformation against the target(s), and identify (using the controlalgorithm(s) and targets) what, if any, adjustments to the stimulationparameters should be made, and then display (either immediately orwhenever called upon to do so) the adjustments in the form ofrecommendations to a physician treating the patient. The physician canthen decide whether to implement the adjustments. If the physiciandecides to implement the adjustment, the physician may accomplish thisby, for example, using a programmer 362 and a part-time communicationlink with the implantable neurostimulator (e.g., inductive telemetryestablished using the inductive wand 364). Determining if anystimulation parameter adjustments need to be made can be done by thephysician while said data management system is not in immediatecommunication with the neurostimulator.

FIG. 19 is a flow chart of systems and methods in which one or moreparameters of a combination therapy including at least a drug therapyand an electrical stimulation therapy may be adjusted in an effort tocontrol the overall result of the combination therapy. In thisembodiment, the drug therapy is a drug therapy including a medicationthe mechanism of action of which is as a sodium channel blocker, and theadjusting of the stimulation parameters is accomplished in an effort tooptimize the therapeutic result for the patient.

In this embodiment, after the medication environment is established(see, e.g., block 1810 of FIG. 18), and the control algorithm(s) andtarget(s) are determined (see, e.g., at block 1820 of FIG. 18), thesystem and method acquire, process, and analyze physiological data andcompare the results of the analyses to the relevant target(s) in orderto assess whether the target(s) is/are met in block 1910. As indicatedin block 1910, acquiring, processing and analyzing physiological datahere includes, at block 1912, counting a number of “detected events”that relate to a particular type of epileptiform activity, andorganizing the counts into one-hour bins, such that the number of timesthe detected event occurs in each of several one-hour periods isdetermined. The acquiring, processing, and analyzing physiological datafurther includes, at block 1914, determining a total number of “detectedevents” counted for a calendar day (i.e., the total count of thedetected events corresponding to the sum of counts in each of 24one-hour bins). This value may be designated a “current day eventcount.” In this embodiment, the target associated with the controlalgorithm may be a target range for the total number of counts of thedetected events per day. For example, the target may be to keep thetotal number of detected events counted per day to 300+/−200 counts perday.

If the system and method deem that the total number of counts of thedetected events per day exceeds the target of 300+/−200, then the targetwill be deemed to not have been met, and, the system and method willdetermine which stimulation parameter, if any, to adjust at block 1920.The system and method will test how far away from the target is to the“current event day count.” More particularly, at block 1922, the“current event day count” will be compared to a count of 500 (i.e., 300counts+/−200 counts). If the “current event day count” is not greaterthan 500, then, at block 1924, the “current event day count” will becompared to a count of 100 (i.e., 300 counts+/−200 counts). If the“current event day count” is less than 100, then (at block 1926) thecontrol algorithm may determine that the “current event day count” isbelow the target of 300 counts+/−200 counts, and that no adjustmentsneed to be made to the set of stimulation parameters.

On the other hand, if at block 1922, the “current event day count” isgreater than 500 then, at block 1930, the control algorithm maydetermine that another stimulation parameter should be checked in orderto decide whether any adjustments to the stimulation parameters shouldbe made. For example, at block 1930, the control algorithm tests whetherthe burst duration that characterizes the present stimulationwaveform(s) is less than one second. If the burst duration is not lessthan one second, then the control algorithm may determine, at block1932, to upwardly adjust (or to recommend adjustment of, as the case maybe) the burst duration by an increment of 100 ms. If the burst durationis not less than one second, then rather than deciding to adjust theburst duration parameter, at block 1936, the control algorithm testswhether the frequency that characterizes the present stimulationwaveform(s) is less than 250 Hz.

If the frequency is not less than 250 Hz, then the control algorithm maydetermine at block 1926 that, even though the “current event day count”is above the target of 300 counts+/−200 counts (i.e., at or above 500counts), no adjustments should be made to the set of stimulationparameters given the values for the present set of stimulationparameters. On the other hand, if the frequency is less than 250 Hz,then the control algorithm may determine, at block 1938, to upwardlyadjust (or to recommend adjustment of, as the case may be) the frequencyby an increment of 25 Hz.

If the “current day event count” is less than 500 but equal or greaterthan 100, as tested by the control algorithm at block 1924, then atblock 1940 the control algorithm tests whether the frequency thatcharacterizes the present stimulation waveform(s) is greater than 100Hz. If the frequency is not greater than 100 Hz, then at block 1950 thecontrol algorithm tests whether the burst duration is greater than 100ms. If the burst duration is greater than 100 ms, then the controlalgorithm may determine, at block 1952, to downwardly adjust (or torecommend adjustment of, as the case may be) the burst duration by adecrement of 100 ms. On the other hand, if the frequency is equal to orless than 100 Hz when tested at block 1940, the control algorithm maydetermine, at block 1942, to downwardly adjust (or to recommendadjustment of) the frequency by a decrement of 25 Hz.

The outcomes of embodiments according to FIG. 19 may correspond to acircumstance in which a low end of a target range can be set for reasonsother than clinical effectiveness; there may be no treatment-relatedreason to adjust settings if fewer than 100 events are counted per day,but it is desirable to reduce stimulation frequency and burst durationwhen lower values may be acceptable in order to conserve neurostimulatorpower and extend battery life. In other embodiments, the target rangemay represent an upper bound, and no parameter adjustments will be madeor recommended by the control algorithm for so long as the measurednumber of counts value falls within or below the target range.

Some or all of the results of execution of the control algorithmdescribed with reference to FIG. 19 may be conveyed to a user via areport viewable on a display, for example, of a host device such as anexternal component (e.g., the programmer or remote monitor 362 or via awebsite interface with a data management system 360), and/or printableby a user. A display or report may be configurable to convey more orless information about the execution of the control algorithm (e.g.,just the stimulation parameter changes, the date and time of each of theparameter changes, or the results of the analysis that led to eachstimulation parameter change or change recommendation), as well as otherinformation, such as information about the medication environment orother stimulation parameter the values of which are not changed (or notrecommended to be changed) by the control algorithm.

FIG. 20 is a flow chart for embodiments of a system and method foroptimizing the parameters according to which electrical stimulationtherapy is delivered to a patient in combination with a drug therapy,based on known information about the parameters of a drug regimen towhich the patient is being subjected. More specifically, in FIG. 20, thedrug regimen includes a medication that modulates the activity of aneurotransmitter such as a GABA receptor agonist.

In this embodiment, after the medication environment is established(see, e.g., block 1810 of FIG. 18), and the control algorithm(s) andtarget(s) are determined (see, e.g., at block 1820 of FIG. 18), thesystem and method acquire, process, and analyze physiological data andcompare the results of the analyses to the relevant target(s) in orderto assess whether the target(s) is/are met in block 2010. As indicatedin block 2010, acquiring, processing and analyzing physiological datahere includes, at block 2012, determining in an electrographic signalbeing monitored from the patient a mean power of the signal in a firstfrequency band, such as the band from about 5 to about 80 Hz, over aperiod of time such as 24 hours. As indicated in block 2010, acquiring,processing and analyzing physiological data here further includes, atblock 2014, determining in an electrographic signal a mean power of thesignal in a second frequency band, such as the band from about 30 toabout 80 Hz, over the same 24-hour period of time as the power in thefirst band was measured. The acquiring, processing, and analyzingphysiological data still further includes, at block 2016, determining aratio of the power in the second band relative to the power in the firstband. In this embodiment, the target associated with the controlalgorithm may be a target value of 0.075+/−0.025 for this power ratio.In other words, the target may be a ratio of the second band to thefirst between 0.1 and 0.05.

If the system and method deem that the power ratio exceeds the target(either by exceeding 0.1 or being less than 0.05), then the target willbe deemed to not have been met, and, the system and method willdetermine whether to and, if so which, stimulation parameter, to adjustat block 2020. The system and method will test how far away from thetarget is the “power ratio.” More particularly, at block 2022, the powerratio will be compared to a power ratio of 0.1. If the power ratio isnot greater than 0.1, then, at block 2024, the power ratio will betested to determine whether it is less than 0.05. If the power ratio isnot less than 0.05, then (at block 2026) the control algorithm maydetermine that the power ratio is within the desired target range forthe power ratio and consequently that no adjustments need to be made tothe set of stimulation parameters.

On the other hand, if the power ratio is greater than 0.1, then at block2028, the control algorithm tests whether the frequency thatcharacterizes the present stimulation waveform(s) is greater than 50 Hz.If the frequency is not greater than 50 Hz, then at block 2030, thecontrol algorithm may determine not to adjust any of the stimulationparameters notwithstanding the fact that the power ratio exceeds theupper limit of the target range for the power ratio. On the other hand,if the frequency is greater than 50 Hz, then at block 2032 the controlalgorithm may determine to downwardly adjust (or to recommend adjustmentof, as the case may be) the frequency by an increment of 25 Hz.

If, at block 2024, the control algorithm determines the power ratio tobe between 0.1 and 0.05, the control algorithm may then test whether thefrequency that characterizes the present stimulation waveform(s) is lessthan 250 Hz. If the frequency is greater than or equal to 250 Hz, thenthe control algorithm may determine not to adjust any of the stimulationparameters (at block 2040). On the other hand, if the frequency is lessthan 250 Hz, the control algorithm may determine to upwardly adjust (orto recommend adjustment of, as the case may be) the frequency by anincrement of 25 Hz (at block 2042).

FIG. 21 is a schematic illustration of a system for facilitation acombination therapy for a patient which combination therapy includes atleast one drug therapy. In an embodiment, one or more leads 114, 116 areimplanted in a patient's brain. Each lead 114, 116 may be provided withelements at a distal portion thereof that may be configured either forsensing physiological data from or delivering a form of stimulation(e.g., stimulation intended to modulate neural activity in one or morestimulation pathways through the neural tissue).

In FIG. 21, the lead 114 is a cortical strip lead 116 with a distalportion 2102. A reservoir 2110 is provided in the distal portion 2102.The reservoir 2110 is configured to be in fluid communication with apermeable or semi-permeable membrane that permits a drug in thereservoir to move into the neural tissue (for example, via a lumen inthe lead or a wall in the lead or otherwise. It will be apparent that asimilar reservoir 2101 may be provided for other types of leads, such asthe depth lead 114 or any other lead configurable to be used withneuromodulation system. The reservoir may be filled with medication and,in some embodiments, can be refilled transcutaneously by injectingmedication through a needle inserted through the patient's scalp andthrough a membrane provided on the reservoir. The permeable orsemi-permeable membrane may be positioned so that medication diffusesfrom the reservoir into the neural tissue and so that the region ofactivity of neurostimulation is at least partially coincident with theregion of activity of the delivered medication. U.S. Pat. No. 7,813,811for “Refillable Reservoir Lead Systems” to Wingeier et al., issued Oct.12, 2010 is directed to subject matter that includes implantablereservoirs for drugs. U.S. Pat. No. 7,813,811 is incorporated byreference in the entirety herein.

It will be apparent that other means for delivery of neurostimulationand medication therapy may be used beneficially with the embodimentsdescribed herein. These other means may include using medicationdelivery devices, such as drug pumps or drug-eluting devices, includingdevices combining the functions of drug pump or drug elution andneurostimulation in a single implanted device. U.S. Pat. No. 7,844,345for “Drug-Eluting Lead Systems” to Boling et al., issued Nov. 30, 2010is directed to subject matter that includes drug-eluting leads. U.S.Pat. No. 7,844,345 is incorporated by reference in the entirety herein.These other means also may include using systems where medication isdelivered via conventional means such as injection or oraladministration but is provided in a kit or on a subscription orrecurring basis with a neurostimulator. Of course, the means may furtherinclude using conventional methods by which medication is delivered suchas injection or oral administration.

Some examples of specific combinations therapies including a drugtherapy and an electrical stimulation therapy are described below.

Example 1

A patient with mesial temporal lobe epilepsy may be treated withresponsive electrical stimulation of the hippocampus, using frequenciessuch as 100 Hz or greater or phase widths such as 200 μs or greater,while delivering the antiepileptic medication levetiracetam at dosagessuch as 1000 to 3000 mg administered orally per day. In otherembodiments, a drug therapy includes delivering levetiracetam usingmeans such as a drug pump or drug-eluting device to maintain a plasmaconcentration known to have effectiveness, such as a plasmaconcentration greater than 11 μg/mL. In alternate embodiments, a drugtherapy includes delivering levetiracetam to the patient in order tofacilitate a patient's response to responsive neurostimulation atdosages below those known to yield effectiveness in medication-onlytreatment, such as 100 to 1000 mg administered orally per day, or atdosages that maintain a plasma concentration below that known to yieldeffectiveness in medication-only treatment, such as plasma concentrationfrom 0.1 to 11 μg/mL. In another embodiment, a drug therapy is deliveredto the seizure focus (in this case, the hippocampus) at concentrationsthat are higher than could be delivered systemically because similarlyhigh concentrations throughout the brain or in the serum would causeunacceptable side effects or even toxicity.

Example 2

A patient with partial onset neocortical epilepsy is treated withresponsive electrical stimulation delivered at or near a neocorticalfocus, using frequencies such as 100 Hz or greater or burst durationssuch as 200 ms or greater, while delivering a sodium channel blockersuch as carbamazepine at dosages such as 800 to 1400 mg administeredorally per day. In other embodiments, a drug therapy includes deliveringcarbamazepine to the patient using means such as a drug pump ordrug-eluting device to maintain a plasma concentration known to haveeffectiveness, such as a plasma concentration greater than 5 μg/mL. Infurther embodiments, carbamazepine is delivered in order to facilitate apatient's response to responsive neurostimulation at dosages below thoseknown to yield effectiveness in medication-only treatment, such as 100to 800 mg administered orally per day, or at dosages that maintain aplasma concentration below that known to yield effectiveness inmedication-only treatment, such as plasma concentration from 0.1 to 5μg/mL. In another embodiment, a drug therapy is delivered to the seizurefocus (in this case, the temporal neocortex) at concentrations that arehigher than could be delivered systemically because similarly highconcentrations throughout the brain or in the serum would causeunacceptable side effects or even toxicity.

Example 3

A patient with partial onset epilepsy is treated with responsiveelectrical stimulation, using frequencies such as 50 to 100 Hz and burstdurations such as less than or equal to 500 ms, while delivering a mixedGABA receptor positive modulator and glutamate receptor antagonist suchas felbamate at dosages such as 1200 to 3600 mg administered orally perday. In other embodiments, a drug therapy includes delivering felbamateto the patient using means such as a drug pump or drug-eluting device tomaintain a plasma concentration known to have effectiveness, such as aplasma concentration greater than 45 μg/mL. In further embodiments,felbamate is delivered in order to facilitate a patient's response toresponsive neurostimulation at dosages below those known to yieldeffectiveness in medication-only treatment, such as 100 to 1200 mgadministered orally per day, or at dosages that maintain a plasmaconcentration below that known to yield effectiveness in medication-onlytreatment, such as plasma concentration from 0.1 to 45 μg/mL. In anotherembodiment, felbamate is delivered to the seizure focus atconcentrations that are higher than could be delivered systemicallybecause similarly high concentrations throughout the brain or in theserum would cause unacceptable side effects or even toxicity such as thewell known life-threatening felbamate-associated toxicity of hepaticnecrosis and aplastic anemia.

Example 4

A patient suffering from migraine headaches is treated with electricalstimulation of the trigeminal nerve or occipital nerve using frequenciessuch as 100 Hz or greater and burst durations such as 200 ms or greater,while delivering a triptan such as sumatriptan when acute symptoms of amigraine headache occur at a dose such as 25 to 100 mg administeredorally. In other embodiments, a drug therapy includes deliveringsumatriptan to the patient when acute symptoms of migraine headacheoccur in order to facilitate a patient's response to neurostimulation atdosages below those known to yield effectiveness in medication-onlytreatment, such as 1 to 25 mg administered orally.

Example 5

A patient with Major Depressive Disorder (MDD) is treated withelectrical stimulation of the subgenual cingulate region usingfrequencies such as 100 Hz or greater and burst durations such as 500 msor less, while delivering a selective serotonin reuptake inhibitor(SSRI) such as fluoxetine at dosages such as 30 to 60 mg administeredorally per day. In other embodiments, a drug therapy includes deliveringfluoxetine at dosages such as 30 to 60 mg administered orally to thepatient per day. In other embodiments, fluoxetine is delivered to thepatient in order to facilitate a patient's response to neurostimulationat dosages below those known to yield effectiveness in medication-onlytreatment, such as 1 to 30 mg administered orally per day. In anotherembodiment, the drug therapy is delivered to the subgenual cingulateregion at concentrations that are higher than could be deliveredsystemically because similarly high concentrations throughout the brainor in the serum would cause unacceptable side effects such as sexualdysfunction and mania.

Example 6

A patient with Parkinson's disease is treated with electricalstimulation of the subthalamic nucleus or internal globus pallidus usingfrequencies such as 130 Hz, while delivering a dopamine agonist such aslevodopa at dosages such as 400 to 800 mg administered orally per day.In other embodiments, a drug therapy includes delivering levodopa to thepatient in order to facilitate a patient's response to neurostimulationat dosages below those known to yield effectiveness in medication-onlytreatment, such as 100 to 400 mg administered orally per day. In anotherembodiment, the drug therapy is delivered to the target atconcentrations that are higher than could be delivered systemicallybecause similarly high concentrations throughout the brain or in theserum would cause unacceptable side effects such as psychosis anddisinhibition.

Example 7

A patient with Alzheimer's disease is treated with electricalstimulation of the fornix using frequencies such as 100 Hz or greaterand burst durations such as 500 ms or less, while delivering acholinergic agonist such as tacrine at dosages such as 80 to 160 mgadministered orally per day. In other embodiments, a drug therapyincluding tacrine is delivered to the patient in order to facilitate apatient's response to neurostimulation at dosages below those known toyield effectiveness in medication-only treatment, such as 10 to 80 mgadministered orally per day. In another embodiment, the drug therapy isdelivered to the target at concentrations that are higher than could bedelivered systemically because similarly high concentrations throughoutthe brain or in the serum would cause unacceptable side effects such aschanges in vision, diarrhea and agitation.

While the foregoing is directed to certain embodiments, other andfurther embodiments may be implemented without departing from the scopeof the present technology, and the scope thereof is determined by theclaims that follow.

What is claimed is:
 1. A method comprising: acquiring physiological datafrom a patient via one or more sensors associated with an implantedmedical device; analyzing with the implanted medical device the acquiredphysiological data to obtain one or more results; determining with theimplanted medical device that a drug therapy to which the patient isbeing subjected is either effective or not effective based on acomparison between at least one of the one or more results and acorresponding baseline or target; in response to determining that thedrug therapy is not effective, delivering with the implanted medicaldevice to one or more locations of interest in the patient's centralnervous system a form of neuromodulation therapy according to at leastone set of programmable neuromodulation parameters, wherein the form ofneuromodulation therapy is different from the drug therapy to which thepatient is being subjected; and repeating the acquiring, analyzing, anddetermining steps with the implanted medical device, and in response todetermining that the drug therapy is not effective, adjusting the atleast one set of programmable neuromodulation parameters, wherein theform of neuromodulation therapy is electrical stimulation, the at leastone set of programmable neuromodulation parameters comprises a set ofelectrical stimulation parameters, and adjusting the at least one set ofprogrammable neuromodulation parameters comprises adjusting the set ofelectrical stimulation parameters based on a mechanism of actionassociated with the drug therapy.
 2. The method of claim 1, wherein theadjusting is performed by the implanted medical device.
 3. The method ofclaim 1, further comprising repeating the acquiring, analyzing,determining, delivering, and adjusting steps until the drug therapy iseffective or until a predetermined time period has been reached orexceeded.
 4. The method of claim 1, wherein the acquired physiologicaldata includes one or more of: electrographic activity sensed from neuraltissue, neurochemical levels, neurotransmitter levels, and extracellularlevels of oxygen.
 5. The method of claim 1, wherein the set ofelectrical stimulation parameters comprises one or more of a phasewidth, a pulse amplitude, an overall pulse morphology, an inter-phaseinterval, a number of pulses in a burst, a burst duration, a burstmorphology, a duty cycle, and a stimulation pathway through the one ormore locations of interest in the patient's central nervous system. 6.The method of claim 1, wherein the mechanism of action is sodium channelblocker and the adjusting comprises increasing one of a burst durationor a frequency of the set of electrical stimulation parameters.
 7. Themethod of claim 1, wherein the mechanism of action is GABA or glutamatemodulator and the adjusting comprises increasing a burst duration ordecreasing a frequency of the set of electrical stimulation parameters.8. The method of claim 1, wherein the mechanism of action is mixed andthe adjusting comprises decreasing a burst duration or increasing afrequency of the set of electrical stimulation parameters.
 9. The methodof claim 1, wherein the mechanism of action is SV2A and the adjustingcomprises increasing one of a current amplitude or a voltage amplitudeof the set of electrical stimulation parameters, or increasing a pulsewidth of the set of electrical stimulation parameters.
 10. The method ofclaim 1, wherein the mechanism of action is dependent on cerebral bloodflow, and the adjusting the at least one set of programmableneuromodulation parameters comprises adjusting the set of electricalstimulation parameters to increase local cerebral blood flow.
 11. Themethod of claim 1, wherein the mechanism of action is dependent oncellular activity, and the adjusting the at least one set ofprogrammable neuromodulation parameters comprises adjusting the set ofelectrical stimulation parameters to increase local neural activity. 12.The method of claim 1, wherein the acquired physiological data compriseselectrographic activity sensed from neural tissue, the implanted medicaldevice is configured to detect an event in the electrographic activitybased on a set of detection parameters, and the one or more resultscomprises at least one of: a count of detected events during a timeperiod, a change in counts of detected events over a plurality of timeperiods, a rate of detected events during a time period, a change inrates of detected events over a plurality of time periods, a statisticalmeasure of durations of detected events during a time period, and achange in statistical measures of durations of detected events over aplurality of time periods.
 13. The method of claim 1, wherein theacquired physiological data comprises electrographic activity sensedfrom neural tissue, the implanted medical device is configured to notean occurrence of a device condition caused by the electrographicactivity, and the one or more results comprises at least one of: a countof occurrences of the device condition during a time period, a change incounts of occurrences of the device condition over a plurality of timeperiods, a rate of occurrences of the device condition during a timeperiod, a change in rates of occurrences of the device condition over aplurality of time periods, a statistical measure of durations ofoccurrences of the device condition during a time period, and a changein statistical measures of durations of occurrences of the devicecondition over a plurality of time periods.
 14. The method of claim 13,wherein the device condition corresponds to a saturation of an amplifierof the implanted medical device.
 15. The method of claim 1, wherein theacquired physiological data comprises electrographic activity sensedfrom neural tissue, the implanted medical device is configured to obtaina measure of power in a frequency band of the electrographic activity,and the one or more results comprises at least one of: measures of powerduring a time period, and a change in measures of power over a pluralityof time periods.
 16. The method of claim 1, wherein the acquiredphysiological data comprises electrographic activity sensed from neuraltissue, the implanted medical device is configured to obtain a measureof evoked potential amplitude in the electrographic activity, and theone or more results comprises at least one of: measures of evokedpotential amplitude during a time period, and a change in measures ofevoked potential amplitude over a plurality of time periods.
 17. Themethod of claim 1, wherein the acquired physiological data comprisesextracellular levels of oxygen, the implanted medical device isconfigured to compare an extracellular level of oxygen to an oxygenthreshold, and the one or more results comprises at least one of: acount of occurrences of the extracellular level of oxygen being belowthe oxygen threshold during a time period, a change in counts of theoccurrences over a plurality of time periods, a rate of counts of theoccurrences during a time period, and a change in rates of counts of theoccurrences over a plurality of time periods.
 18. The method of claim 1,wherein the acquired physiological data comprises neurochemical levels,the implanted medical device is configured to compare a neurochemicallevel to a neurochemical threshold, and the one or more resultscomprises at least one of: a count of occurrences of the neurochemicallevel being below the neurochemical threshold during a time period, achange in counts of the occurrences over a plurality of time periods, arate of counts of the occurrences during a time period, and a change inrates of counts of the occurrences over a plurality of time periods. 19.The method of claim 1, wherein the acquired physiological data comprisesneurotransmitter levels, the implanted medical device is configured tocompare a neurotransmitter level to a neurotransmitter threshold, andthe one or more results comprises at least one of: a count ofoccurrences of the neurotransmitter level being above theneurotransmitter threshold during a time period, a change in counts ofthe occurrences over a plurality of time periods, a rate of counts ofthe occurrences during a time period, and a change in rates of counts ofthe occurrences over a plurality of time periods.
 20. An implantablemedical device comprising: one or more sensors configured to acquirephysiological data from a patient; a neurostimulator configured todeliver a form of neuromodulation therapy to the patient through one ormore stimulation elements; and a processor coupled to the one or moresensors and the neurostimulator and configured to: analyze the acquiredphysiological data to obtain one or more results; determine that a drugtherapy to which the patient is being subjected is either effective ornot effective based on a comparison between at least one of the one ormore results and a corresponding baseline or target; in response todetermining that the drug therapy is not effective, deliver through theneurostimulator to one or more locations of interest in the patient'scentral nervous system, the form of neuromodulation therapy according toat least one set of programmable neuromodulation parameters; and repeatthe acquiring, analyzing, and determining, and in response todetermining that the drug therapy is not effective, adjust the at leastone set of programmable neuromodulation parameters, wherein the form ofneuromodulation therapy is electrical stimulation, the at least one setof programmable neuromodulation parameters comprises a set of electricalstimulation parameters, and the processor is configured to adjust the atleast one set of programmable neuromodulation parameters by adjustingthe set of electrical stimulation parameters based on a mechanism ofaction associated with the drug therapy.
 21. The device of claim 20,wherein the processor is further configured to repeat the acquiring,analyzing, determining, delivering, and adjusting until the drug therapyis effective or until a predetermined time period has been reached orexceeded.
 22. The device of claim 20, wherein the set of electricalstimulation parameters comprises one or more of a phase width, a pulseamplitude, an overall pulse morphology, an inter-phase interval, anumber of pulses in a burst, a burst duration, a burst morphology, aduty cycle, and a stimulation pathway through the one or more locationsof interest in the patient's central nervous system.
 23. The device ofclaim 20, wherein the acquired physiological data compriseselectrographic activity sensed from neural tissue, the processor isconfigured to detect an event in the electrographic activity based on aset of detection parameters, and the one or more results comprises atleast one of: a count of detected events during a time period, a changein counts of detected events over a plurality of time periods, a rate ofdetected events during a time period, a change in rates of detectedevents over a plurality of time periods, a statistical measure ofdurations of detected events during a time period, and a change instatistical measures of durations of detected events over a plurality oftime periods.
 24. The device of claim 20, wherein the acquiredphysiological data comprises electrographic activity sensed from neuraltissue, the processor is configured to note an occurrence of a devicecondition caused by the electrographic activity, and the one or moreresults comprises at least one of: a count of occurrences of the devicecondition during a time period, a change in counts of occurrences of thedevice condition over a plurality of time periods, a rate of occurrencesof the device condition during a time period, a change in rates ofoccurrences of the device condition over a plurality of time periods, astatistical measure of durations of occurrences of the device conditionduring a time period, and a change in statistical measures of durationsof occurrences of the device condition over a plurality of time periods.25. The device of claim 20, wherein the acquired physiological datacomprises electrographic activity sensed from neural tissue, theprocessor is configured to obtain a measure of power in a frequency bandof the electrographic activity, and the one or more results comprises atleast one of: measures of power during a time period, and a change inmeasures of power over a plurality of time periods.
 26. The device ofclaim 20, wherein the acquired physiological data compriseselectrographic activity sensed from neural tissue, the processor isconfigured to obtain a measure of evoked potential amplitude in theelectrographic activity, and the one or more results comprises at leastone of: measures of evoked potential amplitude during a time period, anda change in measures of evoked potential amplitude over a plurality oftime periods.
 27. The device of claim 20, wherein the acquiredphysiological data comprises extracellular levels of oxygen, theprocessor is configured to compare an extracellular level of oxygen toan oxygen threshold, and the one or more results comprises at least oneof: a count of occurrences of the extracellular level of oxygen beingbelow the oxygen threshold during a time period, a change in counts ofthe occurrences over a plurality of time periods, a rate of counts ofthe occurrences during a time period, and a change in rates of counts ofthe occurrences over a plurality of time periods.
 28. The device ofclaim 20, wherein the acquired physiological data comprisesneurochemical levels, the processor is configured to compare aneurochemical level to a neurochemical threshold, and the one or moreresults comprises at least one of: a count of occurrences of theneurochemical level being below the neurochemical threshold during atime period, a change in counts of the occurrences over a plurality oftime periods, a rate of counts of the occurrences during a time period,and a change in rates of counts of the occurrences over a plurality oftime periods.
 29. The device of claim 20, wherein the acquiredphysiological data comprises neurotransmitter levels, the processor isconfigured to compare a neurotransmitter level to a neurotransmitterthreshold, and the one or more results comprises at least one of: acount of occurrences of the neurotransmitter level being above theneurotransmitter threshold during a time period, a change in counts ofthe occurrences over a plurality of time periods, a rate of counts ofthe occurrences during a time period, and a change in rates of counts ofthe occurrences over a plurality of time periods.